Extensions

CEF extensions let you register custom JavaScript that is available globally in every webview. Unlike preload scripts, extensions are registered once at startup and become part of the V8 JavaScript context itself.

Registering Extensions

Pass CefExtensions to CefPlugin during app setup:

use bevy::prelude::*;
use bevy_cef::prelude::*;

fn main() {
    App::new()
        .add_plugins((
            DefaultPlugins,
            CefPlugin {
                extensions: CefExtensions::new().add(
                    "myGame",
                    r#"
                    var myGame = {
                        version: "1.0.0",
                        sendScore: function(score) {
                            window.cef.emit('score_update', { score: score });
                        },
                        getPlayerName: function() {
                            return "Player1";
                        }
                    };
                    "#,
                ),
                ..Default::default()
            },
        ))
        .add_systems(Startup, (spawn_camera, spawn_webview))
        .run();
}

With this extension registered, every webview can call myGame.sendScore(100) or myGame.getPlayerName() directly.

Combining with JS Emit

Extensions work well with the IPC system. Define extension functions that call window.cef.emit(), then handle those events in Bevy:

// In your app setup, register the JsEmitEventPlugin for your event type
app.add_plugins(JsEmitEventPlugin::<ScoreUpdate>::new("score_update"));

// Define the event struct
#[derive(Deserialize)]
struct ScoreUpdate {
    score: u32,
}

// Handle the event with an observer
fn on_score_update(trigger: Trigger<Receive<ScoreUpdate>>) {
    let score = trigger.event().payload.score;
    println!("Score updated: {score}");
}

In the browser, calling myGame.sendScore(42) fires the score_update event, which the Bevy observer receives.

Global Scope

Extensions are registered via CEF's register_extension in the render process and apply to all webviews. You cannot register different extensions for different webviews. If you need per-webview customization, use Preload Scripts instead.

Multiple Extensions

Chain .add() calls to register multiple extensions:

CefExtensions::new()
    .add("myGame", r#"var myGame = { /* ... */ };"#)
    .add("analytics", r#"var analytics = { /* ... */ };"#)

caution

Extension code runs in the V8 context and must be valid JavaScript. Syntax errors in extensions will prevent the render process from initializing correctly.