Implement JavaScript runtime

Cargo.toml

@@ -14,6 +14,7 @@ keywords = ["bevy", "lua", "scripting", "game", "script"]
 lua = ["dep:mlua", "mlua/luajit"]
 rhai = ["dep:rhai"]
 ruby = ["dep:magnus", "dep:rb-sys"]
+javascript = ["dep:deno_core"]
 
 [dependencies]
 bevy = { default-features = false, version = "0.18", features = ["bevy_asset", "bevy_log"] }
@@ -33,6 +34,7 @@ mlua = { version = "0.9.8", features = [
 ], optional = true }
 magnus = { version = "0.8.2", optional = true }
 rb-sys = { version = "0.9", default-features = false, features = ["link-ruby", "ruby-static"], optional = true }
+deno_core = { version = "0.403", optional = true }
 crossbeam-channel = "0.5.15"
 libc = "0.2.172"
 
@@ -211,6 +213,56 @@ name = "side_effects_ruby"
 path = "examples/ruby/side_effects.rs"
 required-features = ["ruby"]
 
+[[example]]
+name = "call_function_from_rust_js"
+path = "examples/js/call_function_from_rust.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "current_entity_js"
+path = "examples/js/current_entity.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "ecs_js"
+path = "examples/js/ecs.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "entity_variable_js"
+path = "examples/js/entity_variable.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "function_params_js"
+path = "examples/js/function_params.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "hello_world_js"
+path = "examples/js/hello_world.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "multiple_plugins_js"
+path = "examples/js/multiple_plugins.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "non_closure_system_js"
+path = "examples/js/non_closure_system.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "promises_js"
+path = "examples/js/promises.rs"
+required-features = ["javascript"]
+
+[[example]]
+name = "side_effects_js"
+path = "examples/js/side_effects.rs"
+required-features = ["javascript"]
+
 [dev-dependencies]
 tracing-subscriber = "0.3.18"
 mlua = { version = "0.9.8", features = ["luajit", "vendored", "send"] }

README.md

@@ -10,6 +10,7 @@ bevy_scriptum is a a plugin for [Bevy](https://bevyengine.org/) that allows you
 | 🌙 LuaJIT                                            | `lua`         | [link](https://jarkonik.github.io/bevy_scriptum/lua/lua.html)   |
 | 🌾 Rhai                                              | `rhai`        | [link](https://jarkonik.github.io/bevy_scriptum/rhai/rhai.html) |
 | 💎 Ruby(currently only supported on Linux and MacOS) | `ruby`        | [link](https://jarkonik.github.io/bevy_scriptum/ruby/ruby.html) |
+| 🟨 JavaScript (V8 via deno_core)                     | `javascript`  | [link](https://jarkonik.github.io/bevy_scriptum/javascript/javascript.html) |
 
 Documentation book is available [here](https://jarkonik.github.io/bevy_scriptum/) 📖
 

assets/examples/js/call_function_from_rust.js

@@ -0,0 +1,13 @@
+var my_state = {
+	iterations: 0,
+};
+
+function on_update() {
+	my_state.iterations = my_state.iterations + 1;
+	print("on_update called " + my_state.iterations + " times");
+
+	if (my_state.iterations >= 10) {
+		print("calling quit");
+		quit();
+	}
+}

assets/examples/js/current_entity.js

@@ -0,0 +1,7 @@
+// entity is a global variable that is set to the entity that is currently being
+// processed, it is automatically available in all scripts.
+
+// get name of the entity
+get_name(entity).and_then(function (name) {
+	print(name);
+});

assets/examples/js/ecs.js

@@ -0,0 +1 @@
+print_player_names();

assets/examples/js/entity_variable.js

@@ -0,0 +1,3 @@
+// entity is a global variable that is set to the entity that is currently being
+// processed, it is automatically available in all scripts.
+print("Current entity index: " + entity.index);

assets/examples/js/function_params.js

@@ -0,0 +1,4 @@
+fun_without_params();
+fun_with_string_param("hello");
+fun_with_i64_param(5);
+fun_with_multiple_params(5, "hello");

assets/examples/js/hello_world.js

@@ -0,0 +1 @@
+hello_bevy();

assets/examples/js/multiple_plugins_plugin_a.js

@@ -0,0 +1 @@
+hello_from_plugin_a();

assets/examples/js/multiple_plugins_plugin_b.js

@@ -0,0 +1 @@
+hello_from_plugin_b_with_parameters("hello", 42);

assets/examples/js/promises.js

@@ -0,0 +1,3 @@
+get_player_name().and_then(function (name) {
+	print(name);
+});

assets/examples/js/side_effects.js

@@ -0,0 +1 @@
+spawn_entity();

assets/tests/js/call_script_function_that_causes_runtime_error.js

@@ -0,0 +1,3 @@
+function test_func() {
+	throw new Error("intentional runtime error");
+}

assets/tests/js/call_script_function_with_params.js

@@ -0,0 +1,7 @@
+var State = {
+	called_with: null,
+};
+
+function test_func(x) {
+	State.called_with = x;
+}

assets/tests/js/entity_variable.js

@@ -0,0 +1,3 @@
+function test_func() {
+	rust_func(entity.index);
+}

assets/tests/js/entity_variable_eval.js

@@ -0,0 +1,5 @@
+var index = entity.index;
+
+function test_func() {
+	rust_func(index);
+}

assets/tests/js/eval_that_causes_runtime_error.js

@@ -0,0 +1,2 @@
+mark_called();
+throw new Error("intentional runtime error");

assets/tests/js/pass_entity_from_script.js

@@ -0,0 +1,3 @@
+function test_func() {
+	rust_func(entity);
+}

assets/tests/js/pass_vec3_from_script.js

@@ -0,0 +1,3 @@
+function test_func() {
+	rust_func(Vec3(1.5, 2.5, -3.5));
+}

assets/tests/js/pass_vec3_to_script.js

@@ -0,0 +1,6 @@
+function test_func(vec3) {
+	if (vec3.x !== 1.5 || vec3.y !== 2.5 || vec3.z !== -3.5) {
+		throw new Error("unexpected Vec3 components");
+	}
+	mark_success();
+}

assets/tests/js/promise_runtime_error.js

@@ -0,0 +1,5 @@
+function test_func() {
+	rust_func().and_then(function (x) {
+		throw new Error("intentional runtime error");
+	});
+}

assets/tests/js/return_via_promise.js

@@ -0,0 +1,9 @@
+var State = {
+	x: null,
+};
+
+function test_func() {
+	rust_func().and_then(function (x) {
+		State.x = x;
+	});
+}

assets/tests/js/rust_function_gets_called_from_script.js

@@ -0,0 +1,3 @@
+function test_func() {
+	rust_func();
+}

assets/tests/js/rust_function_gets_called_from_script_with_multiple_params.js

@@ -0,0 +1,3 @@
+function test_func() {
+	rust_func(5, "test");
+}

assets/tests/js/rust_function_gets_called_from_script_with_param.js

@@ -0,0 +1,3 @@
+function test_func() {
+	rust_func(5);
+}

assets/tests/js/script_function_gets_called_from_rust.js

@@ -0,0 +1,7 @@
+var State = {
+	times_called: 0,
+};
+
+function test_func() {
+	State.times_called = State.times_called + 1;
+}

assets/tests/js/script_function_gets_called_from_rust_with_multiple_params.js

@@ -0,0 +1,9 @@
+var State = {
+	a_value: null,
+	b_value: null,
+};
+
+function test_func(a, b) {
+	State.a_value = a;
+	State.b_value = b;
+}

assets/tests/js/script_function_gets_called_from_rust_with_single_param.js

@@ -0,0 +1,7 @@
+var State = {
+	a_value: null,
+};
+
+function test_func(a) {
+	State.a_value = a;
+}

assets/tests/js/side_effects.js

@@ -0,0 +1,3 @@
+function test_func() {
+	spawn_entity();
+}

book/src/SUMMARY.md

@@ -19,6 +19,15 @@
     - [Calling Ruby from Rust](./ruby/calling_script_from_rust.md)
     - [Interacting with bevy in callbacks](./ruby/interacting_with_bevy.md)
     - [Builtin types](./ruby/builtin_types.md)
+  - [JavaScript](./javascript/javascript.md)
+    - [Installation](./javascript/installation.md)
+    - [Hello World](./javascript/hello_world.md)
+    - [Spawning scripts](./javascript/spawning_scripts.md)
+    - [Calling Rust from JavaScript](./javascript/calling_rust_from_script.md)
+    - [Calling JavaScript from Rust](./javascript/calling_script_from_rust.md)
+    - [Interacting with bevy in callbacks](./javascript/interacting_with_bevy.md)
+    - [Builtin types](./javascript/builtin_types.md)
+    - [Builtin variables](./javascript/builtin_variables.md)
   - [Rhai](./rhai/rhai.md)
     - [Installation](./rhai/installation.md)
     - [Hello World(TBD)]()

book/src/javascript/builtin_types.md

@@ -0,0 +1,85 @@
+# Builtin types
+
+bevy_scriptum provides the following types that can be used in JavaScript:
+
+- `Vec3`
+- `Entity`
+
+## Vec3
+
+A `Vec3` is represented as a plain object with `x`, `y` and `z` number
+properties. A global `Vec3(x, y, z)` constructor function is available to all
+scripts.
+
+### Example JavaScript usage
+
+```js
+var my_vec = Vec3(1, 2, 3);
+print(my_vec.x, my_vec.y, my_vec.z);
+set_translation(entity, my_vec);
+```
+
+### Example Rust usage
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+             runtime.add_function(String::from("set_translation"), set_translation);
+        })
+        .run();
+}
+
+fn set_translation(
+    In((entity, translation)): In<(BevyEntity, BevyVec3)>,
+    mut entities: Query<&mut Transform>,
+) {
+    let mut transform = entities.get_mut(entity.0).unwrap();
+    transform.translation = translation.0;
+}
+```
+
+## Entity
+
+The currently processed entity is available through the global `entity`
+variable. It exposes an `index` property and can be passed back to Rust
+functions that accept a `BevyEntity` argument.
+
+`entity` is currently not available within promise callbacks.
+
+### Example JavaScript usage
+
+```js
+print(entity.index);
+pass_to_rust(entity);
+```
+
+### Example Rust usage
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+             runtime.add_function(String::from("pass_to_rust"), |In((entity,)): In<(BevyEntity,)>| {
+               println!("pass_to_rust called with entity: {:?}", entity);
+             });
+        })
+        .run();
+}
+```

book/src/javascript/builtin_variables.md

@@ -0,0 +1,14 @@
+# Builtin variables
+
+## entity
+
+A variable called `entity` is automatically available to all scripts - it
+represents the bevy entity that the `Script` component is attached to.
+It exposes an `index` property that returns the bevy entity index.
+It is useful for accessing the entity's components from scripts.
+It can be used in the following way:
+```js
+print("Current entity index: " + entity.index);
+```
+
+The `entity` variable is currently not available within promise callbacks.

book/src/javascript/calling_rust_from_script.md

@@ -0,0 +1,113 @@
+# Calling Rust from JavaScript
+
+To call a rust function from JavaScript first you need to register a function
+within Rust using the builder pattern.
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            // `runtime` is a builder that you can use to register functions
+        })
+        .run();
+}
+```
+
+For example to register a function called `my_rust_func` you can do the following:
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+             runtime.add_function(String::from("my_rust_func"), || {
+               println!("my_rust_func has been called");
+             });
+        })
+        .run();
+}
+```
+
+After you do that the function will be available to JavaScript code in your
+spawned scripts.
+
+```js
+my_rust_func();
+```
+
+Since a registered callback function is a Bevy system, the parameters are passed
+to it as an `In` struct with a tuple, which has to be the first parameter of the
+closure.
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+             runtime.add_function(String::from("func_with_params"), |In((a, b)): In<(String, i64)>| {
+               println!("func_with_params has been called with string {} and i64 {}", a, b);
+             });
+        })
+        .run();
+}
+```
+
+The above function can be called from JavaScript
+
+```js
+func_with_params("abc", 123);
+```
+
+## Return value via promise
+
+Any registered rust function that returns a value will return a promise when
+called within a script. By calling `and_then` on the promise you can register
+a callback that will receive the value returned from the Rust function.
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+             runtime.add_function(String::from("returns_value"), || {
+                123
+             });
+        })
+        .run();
+}
+```
+
+```js
+returns_value().and_then(function (value) {
+    print(value); // 123
+});
+```

book/src/javascript/calling_script_from_rust.md

@@ -0,0 +1,66 @@
+# Calling JavaScript from Rust
+
+To call a function defined in JavaScript
+
+```js
+function on_update() {
+}
+```
+
+We need to acquire the `JsRuntime` resource within a bevy system.
+Then we will be able to call `call_fn` on it, providing the name
+of the function to call, the `JsScriptData` that has been automatically
+attached to the entity after an entity with a script attached has been spawned
+and its script evaluated, the entity and optionally some arguments.
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn call_js_on_update_from_rust(
+    mut scripted_entities: Query<(Entity, &mut JsScriptData)>,
+    scripting_runtime: ResMut<JsRuntime>,
+) {
+    for (entity, mut script_data) in &mut scripted_entities {
+        // calling function named `on_update` defined in JavaScript script
+        scripting_runtime
+            .call_fn("on_update", &mut script_data, entity, ())
+            .unwrap();
+    }
+}
+```
+
+We can also pass some arguments by providing a tuple or `Vec` as the last
+`call_fn` argument.
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn call_js_on_update_from_rust(
+    mut scripted_entities: Query<(Entity, &mut JsScriptData)>,
+    scripting_runtime: ResMut<JsRuntime>,
+) {
+    for (entity, mut script_data) in &mut scripted_entities {
+        scripting_runtime
+            .call_fn("on_update", &mut script_data, entity, (123, String::from("hello")))
+            .unwrap();
+    }
+}
+```
+
+They will be passed to the `on_update` JavaScript function
+```js
+function on_update(a, b) {
+    print(a); // 123
+    print(b); // hello
+}
+```

book/src/javascript/hello_world.md

@@ -0,0 +1,75 @@
+# Hello World
+
+After you are done installing the required crates, you can start developing
+your first game or application using bevy_scriptum.
+
+To start using the library you need to first import some structs and traits
+with Rust `use` statements.
+
+For convenience there is a main "prelude" module provided called
+`bevy_scriptum::prelude` and a prelude for each runtime you have enabled as
+a crate feature.
+
+You can now start exposing functions to the scripting language. For example, you
+can expose a function that prints a message to the console:
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+           runtime.add_function(
+               String::from("my_print"),
+               |In((x,)): In<(String,)>| {
+                   println!("my_print: '{}'", x);
+               },
+           );
+        })
+        .run();
+}
+```
+
+Then you can create a script file in `assets` directory called `script.js` that
+calls this function:
+
+```js
+my_print("Hello world!");
+```
+
+And spawn an entity with attached `Script` component with a handle to a script
+source file:
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+           runtime.add_function(
+               String::from("my_print"),
+               |In((x,)): In<(String,)>| {
+                   println!("my_print: '{}'", x);
+               },
+           );
+        })
+        .add_systems(Startup,|mut commands: Commands, asset_server: Res<AssetServer>| {
+            commands.spawn(Script::<JsScript>::new(asset_server.load("script.js")));
+        })
+        .run();
+}
+```
+
+You should then see `my_print: 'Hello world!'` printed in your console.

book/src/javascript/installation.md

@@ -0,0 +1,18 @@
+# Installation
+
+JavaScript support links against V8 which is downloaded as a prebuilt static
+library by the `v8` crate during the build, so the first build may take a while
+and requires network access.
+
+## Main Library
+
+Add the following to your `Cargo.toml`:
+
+```toml
+[dependencies]
+bevy = "0.18"
+bevy_scriptum = { version = "0.11", features = ["javascript"] }
+```
+
+If you need a different version of bevy you need to use a matching bevy_scriptum
+version according to the [bevy support matrix](../bevy_support_matrix.md)

book/src/javascript/interacting_with_bevy.md

@@ -0,0 +1,83 @@
+# Interacting with bevy in callbacks
+
+Every registered function is also just a regular Bevy system.
+
+That allows you to do anything you would do in a Bevy system.
+
+You could for example create a callback system function that prints names
+of all entities with a `Player` component.
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_ecs;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+#[derive(Component)]
+struct Player;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(
+                String::from("print_player_names"),
+                |players: Query<&Name, With<Player>>| {
+                    for player in &players {
+                        println!("player name: {}", player);
+                    }
+                },
+            );
+        })
+        .run();
+}
+```
+
+In script:
+
+```js
+print_player_names();
+```
+
+You can use functions that interact with Bevy entities and resources and
+take arguments at the same time. It could be used for example to mutate a
+component.
+
+```rust,no_run
+# extern crate bevy;
+# extern crate bevy_ecs;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+#[derive(Component)]
+struct Player {
+    health: i32
+}
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(
+                String::from("hurt_player"),
+                |In((hit_value,)): In<(i32,)>, mut players: Query<&mut Player>| {
+                    let mut player = players.single_mut().unwrap();
+                    player.health -= hit_value;
+                },
+            );
+        })
+        .run();
+}
+```
+
+And it could be called in script like:
+
+```js
+hurt_player(5);
+```

book/src/javascript/javascript.md

@@ -0,0 +1,11 @@
+# JavaScript
+
+This chapter demonstrates how to work with bevy_scriptum when using the
+JavaScript language runtime.
+
+JavaScript support is powered by the [V8](https://v8.dev/) engine through
+[`deno_core`](https://crates.io/crates/deno_core). Scripts run synchronously -
+the JavaScript event loop is not pumped, so APIs such as `setTimeout` or native
+`Promise`s are not available. Return values from registered Rust functions are
+delivered through bevy_scriptum's own promise object (see
+[Calling Rust from JavaScript](./calling_rust_from_script.md)).

book/src/javascript/spawning_scripts.md

@@ -0,0 +1,42 @@
+# Spawning scripts
+
+To spawn a JavaScript script you will need to get a handle to a script asset
+using bevy's `AssetServer`.
+
+```rust
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn my_spawner(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("my_script.js"),
+    ));
+}
+```
+
+After the scripts have been evaled by bevy_scriptum, the entities that they've
+been attached to will get the `Script::<JsScript>` component stripped and instead
+a `JsScriptData` component will be attached.
+
+So to query scripted entities you could do something like:
+
+```rust
+# extern crate bevy;
+# extern crate bevy_scriptum;
+
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn my_system(
+    mut scripted_entities: Query<(Entity, &mut JsScriptData)>,
+) {
+    for (entity, mut script_data) in &mut scripted_entities {
+        // do something with scripted entities
+    }
+}
+```

examples/js/call_function_from_rust.rs

@@ -0,0 +1,33 @@
+use bevy::{app::AppExit, prelude::*};
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_systems(Startup, startup)
+        .add_systems(Update, call_js_on_update_from_rust)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(String::from("quit"), |mut exit: MessageWriter<AppExit>| {
+                exit.write(AppExit::Success);
+            });
+        })
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/call_function_from_rust.js"),
+    ));
+}
+
+fn call_js_on_update_from_rust(
+    mut scripted_entities: Query<(Entity, &mut JsScriptData)>,
+    scripting_runtime: ResMut<JsRuntime>,
+) {
+    for (entity, mut script_data) in &mut scripted_entities {
+        scripting_runtime
+            .call_fn("on_update", &mut script_data, entity, ())
+            .unwrap();
+    }
+}

examples/js/current_entity.rs

@@ -0,0 +1,25 @@
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(
+                String::from("get_name"),
+                |In((BevyEntity(entity),)): In<(BevyEntity,)>, names: Query<&Name>| {
+                    names.get(entity).unwrap().to_string()
+                },
+            );
+        })
+        .add_systems(Startup, startup)
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn((
+        Name::from("MyEntityName"),
+        Script::<JsScript>::new(assets_server.load("examples/js/current_entity.js")),
+    ));
+}

examples/js/ecs.rs

@@ -0,0 +1,33 @@
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+#[derive(Component)]
+struct Player;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(
+                String::from("print_player_names"),
+                |players: Query<&Name, With<Player>>| {
+                    for player in &players {
+                        println!("player name: {}", player);
+                    }
+                },
+            );
+        })
+        .add_systems(Startup, startup)
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn((Player, Name::new("John")));
+    commands.spawn((Player, Name::new("Mary")));
+    commands.spawn((Player, Name::new("Alice")));
+
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/ecs.js"),
+    ));
+}

examples/js/entity_variable.rs

@@ -0,0 +1,17 @@
+use bevy::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+use bevy_scriptum::{BuildScriptingRuntime, prelude::*};
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|_| {})
+        .add_systems(Startup, startup)
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/entity_variable.js"),
+    ));
+}

examples/js/function_params.rs

@@ -0,0 +1,40 @@
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime
+                .add_function(String::from("fun_without_params"), || {
+                    println!("called without params");
+                })
+                .add_function(
+                    String::from("fun_with_string_param"),
+                    |In((x,)): In<(String,)>| {
+                        println!("called with string: '{}'", x);
+                    },
+                )
+                .add_function(
+                    String::from("fun_with_i64_param"),
+                    |In((x,)): In<(i64,)>| {
+                        println!("called with i64: {}", x);
+                    },
+                )
+                .add_function(
+                    String::from("fun_with_multiple_params"),
+                    |In((x, y)): In<(i64, String)>| {
+                        println!("called with i64: {} and string: '{}'", x, y);
+                    },
+                );
+        })
+        .add_systems(Startup, startup)
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/function_params.js"),
+    ));
+}

examples/js/hello_world.rs

@@ -0,0 +1,21 @@
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(String::from("hello_bevy"), || {
+                println!("hello bevy, called from script");
+            });
+        })
+        .add_systems(Startup, startup)
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/hello_world.js"),
+    ));
+}

examples/js/multiple_plugins.rs

@@ -0,0 +1,67 @@
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+// Plugin A
+struct PluginA;
+impl Plugin for PluginA {
+    fn build(&self, app: &mut App) {
+        app.add_scripting_api::<JsRuntime>(|runtime| {
+            runtime.add_function(String::from("hello_from_plugin_a"), || {
+                info!("Hello from Plugin A");
+            });
+        })
+        .add_systems(Startup, plugin_a_startup);
+    }
+}
+
+fn plugin_a_startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/multiple_plugins_plugin_a.js"),
+    ));
+}
+
+// Plugin B
+struct PluginB;
+impl Plugin for PluginB {
+    fn build(&self, app: &mut App) {
+        app.add_scripting_api::<JsRuntime>(|runtime| {
+            runtime.add_function(
+                String::from("hello_from_plugin_b_with_parameters"),
+                hello_from_b,
+            );
+        })
+        .add_systems(Startup, plugin_b_startup);
+    }
+}
+
+fn plugin_b_startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/multiple_plugins_plugin_b.js"),
+    ));
+}
+
+fn hello_from_b(In((text, x)): In<(String, i32)>) {
+    info!("{} from Plugin B: {}", text, x);
+}
+
+// Main
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(String::from("hello_bevy"), || {
+                info!("hello bevy, called from script");
+            });
+        })
+        .add_systems(Startup, main_startup)
+        .add_plugins(PluginA)
+        .add_plugins(PluginB)
+        .run();
+}
+
+fn main_startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/hello_world.js"),
+    ));
+}

examples/js/non_closure_system.rs

@@ -0,0 +1,23 @@
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(String::from("hello_bevy"), hello_bevy_callback_system);
+        })
+        .add_systems(Startup, startup)
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/hello_world.js"),
+    ));
+}
+
+fn hello_bevy_callback_system() {
+    println!("hello bevy, called from script");
+}

examples/js/promises.rs

@@ -0,0 +1,31 @@
+use bevy::prelude::*;
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+#[derive(Component)]
+struct Player;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_scripting::<JsRuntime>(|builder| {
+            builder.add_function(
+                String::from("get_player_name"),
+                |player_names: Query<&Name, With<Player>>| {
+                    player_names
+                        .single()
+                        .expect("Missing player_names")
+                        .to_string()
+                },
+            );
+        })
+        .add_systems(Startup, startup)
+        .run();
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn((Player, Name::new("John")));
+    commands.spawn(Script::<JsScript>::new(
+        assets_server.load("examples/js/promises.js"),
+    ));
+}

examples/js/side_effects.rs

@@ -0,0 +1,43 @@
+use bevy::{app::AppExit, prelude::*};
+use bevy_scriptum::prelude::*;
+use bevy_scriptum::runtimes::javascript::prelude::*;
+
+fn main() {
+    App::new()
+        // This is just needed for headless console app, not needed for a regular bevy application
+        // that uses a winit window
+        .set_runner(move |mut app: App| {
+            loop {
+                app.update();
+                if let Some(exit) = app.should_exit() {
+                    return exit;
+                }
+            }
+        })
+        .add_plugins(DefaultPlugins)
+        .add_systems(Startup, startup)
+        .add_systems(Update, print_entity_names_and_quit)
+        .add_scripting::<JsRuntime>(|runtime| {
+            runtime.add_function(String::from("spawn_entity"), spawn_entity);
+        })
+        .run();
+}
+
+fn spawn_entity(mut commands: Commands) {
+    commands.spawn(Name::new("SpawnedEntity"));
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn((Script::<JsScript>::new(
+        assets_server.load("examples/js/side_effects.js"),
+    ),));
+}
+
+fn print_entity_names_and_quit(query: Query<&Name>, mut exit: MessageWriter<AppExit>) {
+    if !query.is_empty() {
+        for e in &query {
+            println!("{}", e);
+        }
+        exit.write(AppExit::Success);
+    }
+}

examples/lua/entity_variable.rs

@@ -1,6 +1,6 @@
 use bevy::prelude::*;
 use bevy_scriptum::runtimes::lua::prelude::*;
-use bevy_scriptum::{prelude::*, BuildScriptingRuntime};
+use bevy_scriptum::{BuildScriptingRuntime, prelude::*};
 
 fn main() {
     App::new()

examples/lua/promises.rs

@@ -11,7 +11,12 @@ fn main() {
         .add_scripting::<LuaRuntime>(|builder| {
             builder.add_function(
                 String::from("get_player_name"),
-                |player_names: Query<&Name, With<Player>>| player_names.single().expect("Missing player_names").to_string(),
+                |player_names: Query<&Name, With<Player>>| {
+                    player_names
+                        .single()
+                        .expect("Missing player_names")
+                        .to_string()
+                },
             );
         })
         .add_systems(Startup, startup)

examples/rhai/entity_variable.rs

@@ -1,6 +1,6 @@
 use bevy::prelude::*;
 use bevy_scriptum::runtimes::rhai::prelude::*;
-use bevy_scriptum::{prelude::*, BuildScriptingRuntime};
+use bevy_scriptum::{BuildScriptingRuntime, prelude::*};
 
 fn main() {
     App::new()

examples/rhai/promises.rs

@@ -11,7 +11,12 @@ fn main() {
         .add_scripting::<RhaiRuntime>(|builder| {
             builder.add_function(
                 String::from("get_player_name"),
-                |player_names: Query<&Name, With<Player>>| player_names.single().expect("Missing player_names").to_string(),
+                |player_names: Query<&Name, With<Player>>| {
+                    player_names
+                        .single()
+                        .expect("Missing player_names")
+                        .to_string()
+                },
             );
         })
         .add_systems(Startup, startup)

examples/ruby/entity_variable.rs

@@ -1,6 +1,6 @@
 use bevy::prelude::*;
 use bevy_scriptum::runtimes::ruby::prelude::*;
-use bevy_scriptum::{prelude::*, BuildScriptingRuntime};
+use bevy_scriptum::{BuildScriptingRuntime, prelude::*};
 
 fn main() {
     App::new()

src/assets.rs

@@ -1,9 +1,9 @@
 use std::marker::PhantomData;
 
 use bevy::{
-    asset::{io::Reader, Asset, AssetLoader, LoadContext},
-    tasks::ConditionalSendFuture,
+    asset::{Asset, AssetLoader, LoadContext, io::Reader},
     reflect::TypePath,
+    tasks::ConditionalSendFuture,
 };
 
 /// A loader for script assets.

src/lib.rs

@@ -9,6 +9,7 @@
 //! | 🌙 LuaJIT                                            | `lua`         | [link](https://jarkonik.github.io/bevy_scriptum/lua/lua.html)   |
 //! | 🌾 Rhai                                              | `rhai`        | [link](https://jarkonik.github.io/bevy_scriptum/rhai/rhai.html) |
 //! | 💎 Ruby(currently only supported on Linux and MacOS) | `ruby`        | [link](https://jarkonik.github.io/bevy_scriptum/ruby/ruby.html) |
+//! | 🟨 JavaScript (V8 via deno_core)                     | `javascript`  | [link](https://jarkonik.github.io/bevy_scriptum/javascript/javascript.html) |
 //!
 //! Documentation book is available [here](https://jarkonik.github.io/bevy_scriptum/) 📖
 //!
@@ -266,7 +267,7 @@ use self::{
     systems::{process_new_scripts, reload_scripts},
 };
 
-#[cfg(any(feature = "rhai", feature = "lua"))]
+#[cfg(any(feature = "rhai", feature = "lua", feature = "javascript"))]
 const ENTITY_VAR_NAME: &str = "entity";
 
 /// An error that can occur when internal [ScriptingPlugin] systems are being executed

src/promise.rs

@@ -58,7 +58,12 @@ impl<C: Clone + Send + 'static, V: Send + Clone> Promise<C, V> {
     }
 
     /// Register a callback that will be called when the [Promise] is resolved.
-    #[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+    #[cfg(any(
+        feature = "rhai",
+        feature = "lua",
+        feature = "ruby",
+        feature = "javascript"
+    ))]
     pub(crate) fn then(&mut self, callback: V) -> Self {
         let mut inner = self
             .inner

src/runtimes/javascript.rs

@@ -0,0 +1,776 @@
+use std::{
+    cell::{Cell, RefCell},
+    collections::HashMap,
+    rc::Rc,
+    sync::{Arc, Mutex},
+    thread::{self, JoinHandle},
+};
+
+use bevy::{
+    asset::Asset,
+    ecs::{component::Component, entity::Entity, resource::Resource, schedule::ScheduleLabel},
+    math::Vec3,
+    reflect::TypePath,
+};
+use deno_core::{JsRuntime as DenoRuntime, RuntimeOptions};
+
+pub use deno_core::v8;
+use serde::Deserialize;
+
+use crate::{
+    ENTITY_VAR_NAME, FuncArgs, Runtime, ScriptingError,
+    assets::GetExtensions,
+    callback::{FromRuntimeValueWithEngine, IntoRuntimeValueWithEngine},
+    promise::Promise,
+};
+
+/// Boxed registered callback function as stored on the JavaScript thread.
+type CallbackFn =
+    dyn Fn((), Vec<JsValue>) -> Result<Promise<(), JsValue>, ScriptingError> + 'static;
+
+/// A queue of value ids that have been dropped on another thread and need to be
+/// removed from the value registry the next time the JavaScript thread runs.
+type FreeQueue = Arc<Mutex<Vec<u64>>>;
+
+thread_local! {
+    /// Registry of live `v8::Global` values, keyed by the id carried in a [JsValue].
+    static REGISTRY: RefCell<HashMap<u64, v8::Global<v8::Value>>> = RefCell::new(HashMap::new());
+    /// Registry of pending promises, keyed by the id stored in the script-side
+    /// promise object.
+    static PROMISES: RefCell<HashMap<u64, Promise<(), JsValue>>> = RefCell::new(HashMap::new());
+    /// Registered Rust callback functions, keyed by their script-visible name.
+    static CALLBACKS: RefCell<HashMap<String, Rc<CallbackFn>>> = RefCell::new(HashMap::new());
+    static NEXT_VALUE_ID: Cell<u64> = const { Cell::new(0) };
+    static NEXT_PROMISE_ID: Cell<u64> = const { Cell::new(0) };
+    static FREE_QUEUE: FreeQueue = Arc::new(Mutex::new(Vec::new()));
+}
+
+/// A handle to a value living inside the JavaScript engine.
+///
+/// The actual `v8::Global` is kept in a thread-local registry on the JavaScript
+/// thread - this handle only carries an id (plus a shared free-list so it can be
+/// cleaned up when dropped from any thread), which makes it cheap to `Clone` and
+/// safe to `Send`.
+#[derive(Clone)]
+pub struct JsValue(Arc<JsValueInner>);
+
+struct JsValueInner {
+    id: u64,
+    free: FreeQueue,
+}
+
+impl Drop for JsValueInner {
+    fn drop(&mut self) {
+        if let Ok(mut queue) = self.free.lock() {
+            queue.push(self.id);
+        }
+    }
+}
+
+/// Removes any values that were dropped on other threads from the registry.
+/// Must be called on the JavaScript thread while the isolate is entered.
+fn drain_free_queue() {
+    let ids: Vec<u64> = FREE_QUEUE.with(|queue| {
+        queue
+            .lock()
+            .map(|mut queue| queue.drain(..).collect())
+            .unwrap_or_default()
+    });
+    if !ids.is_empty() {
+        REGISTRY.with(|registry| {
+            let mut registry = registry.borrow_mut();
+            for id in ids {
+                registry.remove(&id);
+            }
+        });
+    }
+}
+
+/// Stores a `v8::Local` value in the registry and returns a [JsValue] handle for it.
+fn store_value(scope: &mut v8::PinScope, local: v8::Local<v8::Value>) -> JsValue {
+    let global = v8::Global::new(scope, local);
+    let id = NEXT_VALUE_ID.with(|next| {
+        let id = next.get();
+        next.set(id + 1);
+        id
+    });
+    REGISTRY.with(|registry| registry.borrow_mut().insert(id, global));
+    let free = FREE_QUEUE.with(|queue| queue.clone());
+    JsValue(Arc::new(JsValueInner { id, free }))
+}
+
+/// Loads the `v8::Local` value referenced by a [JsValue] handle.
+fn load_value<'s>(scope: &mut v8::PinScope<'s, '_>, value: &JsValue) -> v8::Local<'s, v8::Value> {
+    let global = REGISTRY
+        .with(|registry| registry.borrow().get(&value.0.id).cloned())
+        .expect("JsValue referenced a value that is no longer in the registry");
+    v8::Local::new(scope, global)
+}
+
+fn v8_string<'s>(scope: &mut v8::PinScope<'s, '_>, value: &str) -> v8::Local<'s, v8::Value> {
+    v8::String::new(scope, value)
+        .expect("Failed to allocate JavaScript string")
+        .into()
+}
+
+fn global_object<'s>(scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Object> {
+    scope.get_current_context().global(scope)
+}
+
+fn set_entity(scope: &mut v8::PinScope, entity: Entity) {
+    let global = global_object(scope);
+    let key = v8_string(scope, ENTITY_VAR_NAME);
+    let value = BevyEntity(entity).to_v8(scope);
+    global.set(scope, key, value);
+}
+
+fn clear_entity(scope: &mut v8::PinScope) {
+    let global = global_object(scope);
+    let key = v8_string(scope, ENTITY_VAR_NAME);
+    let undefined: v8::Local<v8::Value> = v8::undefined(scope).into();
+    global.set(scope, key, undefined);
+}
+
+/// Wraps a bevy_scriptum [Promise] into a script-side object exposing `and_then`.
+fn promise_to_v8<'s>(
+    scope: &mut v8::PinScope<'s, '_>,
+    promise: Promise<(), JsValue>,
+) -> v8::Local<'s, v8::Value> {
+    let id = NEXT_PROMISE_ID.with(|next| {
+        let id = next.get();
+        next.set(id + 1);
+        id
+    });
+    PROMISES.with(|promises| promises.borrow_mut().insert(id, promise));
+
+    let object = v8::Object::new(scope);
+    let key = v8_string(scope, "and_then");
+    let data: v8::Local<v8::Value> = v8::Number::new(scope, id as f64).into();
+    let function = v8::Function::builder(and_then_callback)
+        .data(data)
+        .build(scope)
+        .expect("Failed to create and_then function");
+    object.set(scope, key, function.into());
+    object.into()
+}
+
+/// `and_then` method on script-side promise objects.
+fn and_then_callback(
+    scope: &mut v8::PinScope,
+    args: v8::FunctionCallbackArguments,
+    mut rv: v8::ReturnValue<v8::Value>,
+) {
+    let id = args
+        .data()
+        .number_value(scope)
+        .expect("Promise object is missing its id") as u64;
+    let callback = store_value(scope, args.get(0));
+
+    let following = PROMISES.with(|promises| {
+        let mut promises = promises.borrow_mut();
+        let promise = promises
+            .get_mut(&id)
+            .expect("Promise referenced by script no longer exists");
+        promise.then(callback)
+    });
+
+    let object = promise_to_v8(scope, following);
+    rv.set(object);
+}
+
+/// Callback invoked by V8 for every registered Rust function.
+fn native_callback(
+    scope: &mut v8::PinScope,
+    args: v8::FunctionCallbackArguments,
+    mut rv: v8::ReturnValue<v8::Value>,
+) {
+    let name = args.data().to_rust_string_lossy(scope);
+
+    let mut params = Vec::with_capacity(args.length() as usize);
+    for i in 0..args.length() {
+        params.push(store_value(scope, args.get(i)));
+    }
+
+    let callback = CALLBACKS.with(|callbacks| callbacks.borrow().get(&name).cloned());
+    if let Some(callback) = callback {
+        let promise = callback((), params).expect("Failed to call registered function");
+        let object = promise_to_v8(scope, promise);
+        rv.set(object);
+    }
+}
+
+fn print_callback(
+    scope: &mut v8::PinScope,
+    args: v8::FunctionCallbackArguments,
+    _rv: v8::ReturnValue<v8::Value>,
+) {
+    let mut parts = Vec::with_capacity(args.length() as usize);
+    for i in 0..args.length() {
+        parts.push(args.get(i).to_rust_string_lossy(scope));
+    }
+    println!("{}", parts.join(" "));
+}
+
+/// `Vec3(x, y, z)` global constructor available to all scripts.
+fn vec3_callback(
+    scope: &mut v8::PinScope,
+    args: v8::FunctionCallbackArguments,
+    mut rv: v8::ReturnValue<v8::Value>,
+) {
+    let component = |scope: &mut v8::PinScope, index: i32| {
+        args.get(index).number_value(scope).unwrap_or(0.0) as f32
+    };
+    let x = component(scope, 0);
+    let y = component(scope, 1);
+    let z = component(scope, 2);
+    let value = BevyVec3::new(x, y, z).to_v8(scope);
+    rv.set(value);
+}
+
+/// Registers a global function on the engine's global object.
+fn register_global_function(
+    scope: &mut v8::PinScope,
+    name: &str,
+    callback: impl v8::MapFnTo<v8::FunctionCallback>,
+) {
+    let global = global_object(scope);
+    let key = v8_string(scope, name);
+    let function = v8::Function::new(scope, callback)
+        .unwrap_or_else(|| panic!("Failed to create `{name}` function"));
+    global.set(scope, key, function.into());
+}
+
+/// Calls a global script function by name with the provided arguments.
+fn call_global_fn(
+    scope: &mut v8::PinScope,
+    name: &str,
+    args: &[JsValue],
+) -> Result<JsValue, ScriptingError> {
+    let global = global_object(scope);
+    let key = v8_string(scope, name);
+    let value = global
+        .get(scope, key)
+        .ok_or_else(|| ScriptingError::RuntimeError(format!("function `{name}` not found")))?;
+    let function = value
+        .try_cast::<v8::Function>()
+        .map_err(|_| ScriptingError::RuntimeError(format!("`{name}` is not a function")))?;
+    let arguments: Vec<v8::Local<v8::Value>> =
+        args.iter().map(|arg| load_value(scope, arg)).collect();
+    call_function(scope, function, &arguments)
+}
+
+/// Calls a `v8::Function` with the provided arguments, capturing runtime errors.
+fn call_function(
+    scope: &mut v8::PinScope,
+    function: v8::Local<v8::Function>,
+    arguments: &[v8::Local<v8::Value>],
+) -> Result<JsValue, ScriptingError> {
+    let recv: v8::Local<v8::Value> = v8::undefined(scope).into();
+    v8::tc_scope!(let scope, scope);
+    match function.call(scope, recv, arguments) {
+        Some(result) => Ok(store_value(scope, result)),
+        None => {
+            let message = scope
+                .exception()
+                .map(|exception| exception.to_rust_string_lossy(scope))
+                .unwrap_or_else(|| String::from("unknown JavaScript error"));
+            Err(ScriptingError::RuntimeError(message))
+        }
+    }
+}
+
+/// The JavaScript engine - a thin wrapper around a deno_core [JsRuntime] that
+/// allows obtaining a V8 scope through a shared reference (the rest of
+/// bevy_scriptum only hands out `&RawEngine`).
+pub struct JsEngine {
+    runtime: RefCell<DenoRuntime>,
+}
+
+impl JsEngine {
+    fn new() -> Self {
+        let engine = Self {
+            runtime: RefCell::new(DenoRuntime::new(RuntimeOptions::default())),
+        };
+        engine.with_scope(|scope| {
+            register_global_function(scope, "print", print_callback);
+            register_global_function(scope, "Vec3", vec3_callback);
+        });
+        engine
+    }
+
+    /// Runs `f` with a V8 handle/context scope ready for use.
+    pub fn with_scope<R>(&self, f: impl FnOnce(&mut v8::PinScope) -> R) -> R {
+        let mut runtime = self.runtime.borrow_mut();
+        let context = runtime.main_context();
+        let isolate = &mut *runtime.v8_isolate();
+        v8::scope!(let scope, isolate);
+        let context = v8::Local::new(scope, context);
+        let scope = &mut v8::ContextScope::new(scope, context);
+        drain_free_queue();
+        f(scope)
+    }
+}
+
+#[derive(Resource)]
+pub struct JsRuntime {
+    thread: Option<JsThread>,
+}
+
+impl Default for JsRuntime {
+    fn default() -> Self {
+        Self {
+            thread: Some(JsThread::spawn()),
+        }
+    }
+}
+
+impl JsRuntime {
+    fn execute_in_thread<T: Send + 'static>(
+        &self,
+        f: impl FnOnce(&mut JsEngine) -> T + Send + 'static,
+    ) -> T {
+        self.thread
+            .as_ref()
+            .expect("JavaScript thread is gone")
+            .execute(Box::new(f))
+    }
+
+    /// Runs `f` with a V8 scope on the JavaScript thread. Useful for directly
+    /// interacting with the engine, e.g. from tests.
+    pub fn with_scope<T: Send + 'static>(
+        &self,
+        f: impl FnOnce(&mut v8::PinScope) -> T + Send + 'static,
+    ) -> T {
+        self.execute_in_thread(move |engine| engine.with_scope(f))
+    }
+}
+
+type JsClosure = Box<dyn FnOnce(&mut JsEngine) + Send>;
+
+/// A dedicated thread owning the (non-`Send`) V8 isolate.
+struct JsThread {
+    sender: Option<crossbeam_channel::Sender<JsClosure>>,
+    handle: Option<JoinHandle<()>>,
+}
+
+impl JsThread {
+    fn spawn() -> Self {
+        let (sender, receiver) = crossbeam_channel::unbounded::<JsClosure>();
+
+        let handle = thread::spawn(move || {
+            let mut engine = JsEngine::new();
+            while let Ok(f) = receiver.recv() {
+                f(&mut engine);
+            }
+        });
+
+        JsThread {
+            sender: Some(sender),
+            handle: Some(handle),
+        }
+    }
+
+    fn execute<T: Send + 'static>(&self, f: Box<dyn FnOnce(&mut JsEngine) -> T + Send>) -> T {
+        let (return_sender, return_receiver) = crossbeam_channel::bounded(1);
+        self.sender
+            .as_ref()
+            .expect("JavaScript thread sender is gone")
+            .send(Box::new(move |engine| {
+                let _ = return_sender.send(f(engine));
+            }))
+            .expect("Failed to send execution unit to JavaScript thread");
+        return_receiver
+            .recv()
+            .expect("Failed to receive callback return value from JavaScript thread")
+    }
+}
+
+impl Drop for JsThread {
+    fn drop(&mut self) {
+        drop(self.sender.take());
+        if let Some(handle) = self.handle.take() {
+            let _ = handle.join();
+        }
+    }
+}
+
+#[derive(ScheduleLabel, Clone, PartialEq, Eq, Debug, Hash, Default)]
+pub struct JsSchedule;
+
+#[derive(Asset, Debug, Deserialize, TypePath)]
+pub struct JsScript(pub String);
+
+impl GetExtensions for JsScript {
+    fn extensions() -> &'static [&'static str] {
+        &["js"]
+    }
+}
+
+impl From<String> for JsScript {
+    fn from(value: String) -> Self {
+        Self(value)
+    }
+}
+
+#[derive(Component)]
+pub struct JsScriptData;
+
+#[derive(Debug, Clone, Copy)]
+pub struct BevyEntity(pub Entity);
+
+impl BevyEntity {
+    pub fn index(&self) -> u32 {
+        self.0.index_u32()
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct BevyVec3(pub Vec3);
+
+impl BevyVec3 {
+    pub fn new(x: f32, y: f32, z: f32) -> Self {
+        Self(Vec3::new(x, y, z))
+    }
+
+    pub fn x(&self) -> f32 {
+        self.0.x
+    }
+
+    pub fn y(&self) -> f32 {
+        self.0.y
+    }
+
+    pub fn z(&self) -> f32 {
+        self.0.z
+    }
+}
+
+impl Runtime for JsRuntime {
+    type Schedule = JsSchedule;
+    type ScriptAsset = JsScript;
+    type ScriptData = JsScriptData;
+    type CallContext = ();
+    type Value = JsValue;
+    type RawEngine = JsEngine;
+
+    fn with_engine_send_mut<T: Send + 'static>(
+        &mut self,
+        f: impl FnOnce(&mut Self::RawEngine) -> T + Send + 'static,
+    ) -> T {
+        self.execute_in_thread(f)
+    }
+
+    fn with_engine_send<T: Send + 'static>(
+        &self,
+        f: impl FnOnce(&Self::RawEngine) -> T + Send + 'static,
+    ) -> T {
+        self.execute_in_thread(move |engine| f(engine))
+    }
+
+    fn with_engine_mut<T>(&mut self, _f: impl FnOnce(&mut Self::RawEngine) -> T) -> T {
+        unimplemented!(
+            "JavaScript runtime requires sending execution to another thread, use `with_engine_send_mut`"
+        );
+    }
+
+    fn with_engine<T>(&self, _f: impl FnOnce(&Self::RawEngine) -> T) -> T {
+        unimplemented!(
+            "JavaScript runtime requires sending execution to another thread, use `with_engine_send`"
+        );
+    }
+
+    fn eval(
+        &self,
+        script: &Self::ScriptAsset,
+        entity: Entity,
+    ) -> Result<Self::ScriptData, ScriptingError> {
+        let source = script.0.clone();
+        self.execute_in_thread(move |engine| {
+            engine.with_scope(|scope| set_entity(scope, entity));
+            let result = engine
+                .runtime
+                .borrow_mut()
+                .execute_script("[bevy_scriptum]", source);
+            engine.with_scope(clear_entity);
+            result
+                .map(|_| JsScriptData)
+                .map_err(|e| ScriptingError::RuntimeError(e.to_string()))
+        })
+    }
+
+    fn register_fn(
+        &mut self,
+        name: String,
+        _arg_types: Vec<std::any::TypeId>,
+        f: impl Fn(
+            Self::CallContext,
+            Vec<Self::Value>,
+        ) -> Result<Promise<Self::CallContext, Self::Value>, ScriptingError>
+        + Send
+        + Sync
+        + 'static,
+    ) -> Result<(), ScriptingError> {
+        self.execute_in_thread(move |engine| {
+            CALLBACKS.with(|callbacks| {
+                callbacks.borrow_mut().insert(name.clone(), Rc::new(f));
+            });
+            engine.with_scope(|scope| {
+                let global = global_object(scope);
+                let key = v8_string(scope, &name);
+                let data = v8_string(scope, &name);
+                let function = v8::Function::builder(native_callback)
+                    .data(data)
+                    .build(scope)
+                    .expect("Failed to create registered function");
+                global.set(scope, key, function.into());
+            });
+        });
+        Ok(())
+    }
+
+    fn call_fn(
+        &self,
+        name: &str,
+        _script_data: &mut Self::ScriptData,
+        entity: Entity,
+        args: impl for<'a> FuncArgs<'a, Self::Value, Self> + Send + 'static,
+    ) -> Result<Self::Value, ScriptingError> {
+        let name = name.to_string();
+        self.execute_in_thread(move |engine| {
+            let args = args.parse(engine);
+            engine.with_scope(|scope| {
+                set_entity(scope, entity);
+                let result = call_global_fn(scope, &name, &args);
+                clear_entity(scope);
+                result
+            })
+        })
+    }
+
+    fn call_fn_from_value(
+        &self,
+        value: &Self::Value,
+        _context: &Self::CallContext,
+        args: Vec<Self::Value>,
+    ) -> Result<Self::Value, ScriptingError> {
+        let value = value.clone();
+        self.execute_in_thread(move |engine| {
+            engine.with_scope(|scope| {
+                let local = load_value(scope, &value);
+                let function = local.try_cast::<v8::Function>().map_err(|_| {
+                    ScriptingError::RuntimeError(String::from("value is not a function"))
+                })?;
+                let arguments: Vec<v8::Local<v8::Value>> =
+                    args.iter().map(|arg| load_value(scope, arg)).collect();
+                call_function(scope, function, &arguments)
+            })
+        })
+    }
+}
+
+/// Conversion from a Rust value into a V8 value.
+trait ToV8 {
+    fn to_v8<'s>(self, scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Value>;
+}
+
+/// Conversion from a V8 value into a Rust value.
+trait FromV8 {
+    fn from_v8(scope: &mut v8::PinScope, value: v8::Local<v8::Value>) -> Self;
+}
+
+macro_rules! impl_number {
+    ($($t:ty),*) => {$(
+        impl ToV8 for $t {
+            fn to_v8<'s>(self, scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Value> {
+                v8::Number::new(scope, self as f64).into()
+            }
+        }
+
+        impl FromV8 for $t {
+            fn from_v8(scope: &mut v8::PinScope, value: v8::Local<v8::Value>) -> Self {
+                value.number_value(scope).unwrap_or(0.0) as $t
+            }
+        }
+    )*};
+}
+
+impl_number!(i8, i16, i32, i64, isize, u8, u16, u32, u64, usize, f32, f64);
+
+impl ToV8 for String {
+    fn to_v8<'s>(self, scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Value> {
+        v8_string(scope, &self)
+    }
+}
+
+impl FromV8 for String {
+    fn from_v8(scope: &mut v8::PinScope, value: v8::Local<v8::Value>) -> Self {
+        value.to_rust_string_lossy(scope)
+    }
+}
+
+impl ToV8 for bool {
+    fn to_v8<'s>(self, scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Value> {
+        v8::Boolean::new(scope, self).into()
+    }
+}
+
+impl FromV8 for bool {
+    fn from_v8(scope: &mut v8::PinScope, value: v8::Local<v8::Value>) -> Self {
+        value.boolean_value(scope)
+    }
+}
+
+impl ToV8 for () {
+    fn to_v8<'s>(self, scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Value> {
+        v8::undefined(scope).into()
+    }
+}
+
+impl FromV8 for () {
+    fn from_v8(_scope: &mut v8::PinScope, _value: v8::Local<v8::Value>) -> Self {}
+}
+
+impl ToV8 for BevyEntity {
+    fn to_v8<'s>(self, scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Value> {
+        let object = v8::Object::new(scope);
+
+        let key = v8_string(scope, "index");
+        let value: v8::Local<v8::Value> =
+            v8::Integer::new_from_unsigned(scope, self.index()).into();
+        object.set(scope, key, value);
+
+        let key = v8_string(scope, "__entity_bits");
+        let value: v8::Local<v8::Value> = v8::BigInt::new_from_u64(scope, self.0.to_bits()).into();
+        object.set(scope, key, value);
+
+        object.into()
+    }
+}
+
+impl FromV8 for BevyEntity {
+    fn from_v8(scope: &mut v8::PinScope, value: v8::Local<v8::Value>) -> Self {
+        let object = value.to_object(scope).expect("entity is not an object");
+        let key = v8_string(scope, "__entity_bits");
+        let bits = object
+            .get(scope, key)
+            .expect("entity object is missing `__entity_bits`")
+            .try_cast::<v8::BigInt>()
+            .expect("`__entity_bits` is not a BigInt");
+        let (bits, _) = bits.u64_value();
+        BevyEntity(Entity::from_bits(bits))
+    }
+}
+
+impl ToV8 for BevyVec3 {
+    fn to_v8<'s>(self, scope: &mut v8::PinScope<'s, '_>) -> v8::Local<'s, v8::Value> {
+        let object = v8::Object::new(scope);
+        for (name, component) in [("x", self.0.x), ("y", self.0.y), ("z", self.0.z)] {
+            let key = v8_string(scope, name);
+            let value: v8::Local<v8::Value> = v8::Number::new(scope, component as f64).into();
+            object.set(scope, key, value);
+        }
+        object.into()
+    }
+}
+
+impl FromV8 for BevyVec3 {
+    fn from_v8(scope: &mut v8::PinScope, value: v8::Local<v8::Value>) -> Self {
+        let object = value.to_object(scope).expect("Vec3 is not an object");
+        let read = |scope: &mut v8::PinScope, name: &str| {
+            let key = v8_string(scope, name);
+            object
+                .get(scope, key)
+                .and_then(|value| value.number_value(scope))
+                .unwrap_or(0.0) as f32
+        };
+        let x = read(scope, "x");
+        let y = read(scope, "y");
+        let z = read(scope, "z");
+        BevyVec3(Vec3::new(x, y, z))
+    }
+}
+
+impl<'a, T: ToV8> IntoRuntimeValueWithEngine<'a, T, JsRuntime> for T {
+    fn into_runtime_value_with_engine(value: T, engine: &'a JsEngine) -> JsValue {
+        engine.with_scope(|scope| {
+            let local = value.to_v8(scope);
+            store_value(scope, local)
+        })
+    }
+}
+
+impl<'a, T: FromV8> FromRuntimeValueWithEngine<'a, JsRuntime> for T {
+    fn from_runtime_value_with_engine(value: JsValue, engine: &'a JsEngine) -> Self {
+        engine.with_scope(|scope| {
+            let local = load_value(scope, &value);
+            T::from_v8(scope, local)
+        })
+    }
+}
+
+impl FuncArgs<'_, JsValue, JsRuntime> for () {
+    fn parse(self, _engine: &JsEngine) -> Vec<JsValue> {
+        Vec::new()
+    }
+}
+
+impl<T: ToV8> FuncArgs<'_, JsValue, JsRuntime> for Vec<T> {
+    fn parse(self, engine: &JsEngine) -> Vec<JsValue> {
+        engine.with_scope(|scope| {
+            self.into_iter()
+                .map(|value| {
+                    let local = value.to_v8(scope);
+                    store_value(scope, local)
+                })
+                .collect()
+        })
+    }
+}
+
+pub mod prelude {
+    pub use super::{BevyEntity, BevyVec3, JsRuntime, JsScript, JsScriptData};
+}
+
+macro_rules! impl_tuple {
+    ($($idx:tt $t:tt),+) => {
+        impl<$($t: ToV8,)+> FuncArgs<'_, JsValue, JsRuntime> for ($($t,)+) {
+            fn parse(self, engine: &JsEngine) -> Vec<JsValue> {
+                engine.with_scope(|scope| {
+                    vec![
+                        $({
+                            let local = self.$idx.to_v8(scope);
+                            store_value(scope, local)
+                        },)+
+                    ]
+                })
+            }
+        }
+    };
+}
+
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S, 19 T, 20 U, 21 V, 22 W, 23 X, 24 Y, 25 Z);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S, 19 T, 20 U, 21 V, 22 W, 23 X, 24 Y);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S, 19 T, 20 U, 21 V, 22 W, 23 X);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S, 19 T, 20 U, 21 V, 22 W);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S, 19 T, 20 U, 21 V);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S, 19 T, 20 U);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S, 19 T);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R, 18 S);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q, 17 R);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P, 16 Q);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O, 15 P);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N, 14 O);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M, 13 N);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L, 12 M);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K, 11 L);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J, 10 K);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I, 9 J);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H, 8 I);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F);
+impl_tuple!(0 A, 1 B, 2 C, 3 D, 4 E);
+impl_tuple!(0 A, 1 B, 2 C, 3 D);
+impl_tuple!(0 A, 1 B, 2 C);
+impl_tuple!(0 A, 1 B);
+impl_tuple!(0 A);

src/runtimes/mod.rs

@@ -1,3 +1,5 @@
+#[cfg(feature = "javascript")]
+pub mod javascript;
 #[cfg(feature = "lua")]
 pub mod lua;
 #[cfg(feature = "rhai")]

tests/tests.rs

@@ -1,17 +1,47 @@
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 use std::sync::OnceLock;
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 use bevy::ecs::system::RunSystemOnce as _;
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 use bevy::prelude::*;
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 use bevy_scriptum::{FuncArgs, Runtime, prelude::*};
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 static TRACING_SUBSCRIBER: OnceLock<()> = OnceLock::new();
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 #[derive(Default, Resource)]
 struct TimesCalled {
     times_called: u8,
@@ -29,7 +59,12 @@ macro_rules! assert_n_times_called {
     };
 }
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 fn build_test_app() -> App {
     let mut app = App::new();
 
@@ -43,7 +78,12 @@ fn build_test_app() -> App {
     app
 }
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 fn run_script<R: Runtime, Out, Marker>(
     app: &mut App,
     path: String,
@@ -60,7 +100,12 @@ fn run_script<R: Runtime, Out, Marker>(
     entity_id
 }
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 fn call_script_on_update_from_rust<R: Runtime>(
     mut scripted_entities: Query<(Entity, &mut R::ScriptData)>,
     scripting_runtime: ResMut<R>,
@@ -73,7 +118,12 @@ fn call_script_on_update_from_rust<R: Runtime>(
         .unwrap();
 }
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 trait AssertStateKeyValue {
     type ScriptData;
     fn assert_state_key_value_i64(world: &World, entity_id: Entity, key: &str, value: i64);
@@ -81,7 +131,12 @@ trait AssertStateKeyValue {
     fn assert_state_key_value_string(world: &World, entity_id: Entity, key: &str, value: &str);
 }
 
-#[cfg(any(feature = "rhai", feature = "lua", feature = "ruby"))]
+#[cfg(any(
+    feature = "rhai",
+    feature = "lua",
+    feature = "ruby",
+    feature = "javascript"
+))]
 macro_rules! scripting_tests {
     ($runtime:ty, $script:literal, $extension:literal, $entity_type: ty, $vec_type: ty) => {
         use super::*;
@@ -712,3 +767,60 @@ mod ruby_tests {
 
     scripting_tests!(RubyRuntime, "ruby", "rb", BevyEntity, BevyVec3);
 }
+
+#[cfg(feature = "javascript")]
+mod javascript_tests {
+    use bevy::prelude::*;
+    use bevy_scriptum::runtimes::javascript::{prelude::*, v8};
+
+    fn with_state_value<T: Send + 'static>(
+        world: &World,
+        key: &str,
+        f: impl FnOnce(&mut v8::PinScope, v8::Local<v8::Value>) -> T + Send + 'static,
+    ) -> T {
+        let runtime = world.get_resource::<JsRuntime>().unwrap();
+        let key = key.to_string();
+        runtime.with_scope(move |scope| {
+            let global = scope.get_current_context().global(scope);
+            let state_key: v8::Local<v8::Value> = v8::String::new(scope, "State").unwrap().into();
+            let state = global
+                .get(scope, state_key)
+                .unwrap()
+                .to_object(scope)
+                .unwrap();
+            let value_key: v8::Local<v8::Value> = v8::String::new(scope, &key).unwrap().into();
+            let value = state.get(scope, value_key).unwrap();
+            f(scope, value)
+        })
+    }
+
+    impl AssertStateKeyValue for JsRuntime {
+        type ScriptData = JsScriptData;
+
+        fn assert_state_key_value_i64(world: &World, _entity_id: Entity, key: &str, value: i64) {
+            let actual = with_state_value(world, key, |scope, val| {
+                val.number_value(scope).unwrap() as i64
+            });
+            assert_eq!(actual, value);
+        }
+
+        fn assert_state_key_value_i32(world: &World, _entity_id: Entity, key: &str, value: i32) {
+            let actual = with_state_value(world, key, |scope, val| {
+                val.number_value(scope).unwrap() as i32
+            });
+            assert_eq!(actual, value);
+        }
+
+        fn assert_state_key_value_string(
+            world: &World,
+            _entity_id: Entity,
+            key: &str,
+            value: &str,
+        ) {
+            let actual = with_state_value(world, key, |scope, val| val.to_rust_string_lossy(scope));
+            assert_eq!(actual, value);
+        }
+    }
+
+    scripting_tests!(JsRuntime, "js", "js", BevyEntity, BevyVec3);
+}