Interaction with browser scripting

When building content for the web, you might need to communicate with other elements on your web page. Or you might want to implement functionality using Web APIs which Unity doesn’t expose by default. In both cases, you need to directly interface with the browser’s JavaScript engine. Unity WebGL provides different methods to do this.

从 Unity 脚本调用 JavaScript 函数

The recommended way of using browser JavaScript in your project is to add your JavaScript sources to your project, and then call those functions directly from your script code. To do so, place files with JavaScript code using the .jslib extension in the Assets folder > Plugins subfolder. The plugin file needs to have a syntax like this:

mergeInto(LibraryManager.library, {

  Hello: function () {
    window.alert("Hello, world!");
  },

  HelloString: function (str) {
    window.alert(UTF8ToString(str));
  },

  PrintFloatArray: function (array, size) {
    for(var i = 0; i < size; i++)
    console.log(HEAPF32[(array >> 2) + i]);
  },

  AddNumbers: function (x, y) {
    return x + y;
  },

  StringReturnValueFunction: function () {
    var returnStr = "bla";
    var bufferSize = lengthBytesUTF8(returnStr) + 1;
    var buffer = _malloc(bufferSize);
    stringToUTF8(returnStr, buffer, bufferSize);
    return buffer;
  },

  BindWebGLTexture: function (texture) {
    GLctx.bindTexture(GLctx.TEXTURE_2D, GL.textures[texture]);
  },

});

Then, you can call these functions from your C# scripts as follows:

using UnityEngine;
using System.Runtime.InteropServices;

public class NewBehaviourScript : MonoBehaviour {

    [DllImport("__Internal")]
    private static extern void Hello();

    [DllImport("__Internal")]
    private static extern void HelloString(string str);

    [DllImport("__Internal")]
    private static extern void PrintFloatArray(float[] array, int size);

    [DllImport("__Internal")]
    private static extern int AddNumbers(int x, int y);

    [DllImport("__Internal")]
    private static extern string StringReturnValueFunction();

    [DllImport("__Internal")]
    private static extern void BindWebGLTexture(int texture);

    void Start() {
        Hello();
        
        HelloString("This is a string.");
        
        float[] myArray = new float[10];
        PrintFloatArray(myArray, myArray.Length);
        
        int result = AddNumbers(5, 7);
        Debug.Log(result);
        
        Debug.Log(StringReturnValueFunction());
        
        var texture = new Texture2D(1, 1, TextureFormat.ARGB32, false);
        BindWebGLTexture(texture.GetNativeTexturePtr());
    }
}

More Details:

• You can pass simple numeric types to JavaScript in function parameters without doing any conversion. You can pass other data types as a pointer in the emscripten heap which is just a big array in JavaScript.
• For strings, you can use the UTF8ToString helper function to convert to a JavaScript string.
• To return a string value, call _malloc to allocate some memory and the stringToUTF8 helper function to write a JavaScript string to it. If the string is a return value, then the IL2CPP runtime automatically frees up the memory for you.
• For arrays of primitive types, emscripten provides different ArrayBufferViews into its heap for different sizes of integer, unsigned integer or floating point representations of memory: HEAP8, HEAPU8, HEAP16, HEAPU16, HEAP32, HEAPU32, HEAPF32, HEAPF64.
• To access a texture in WebGL, emscripten provides the GL.textures array which maps native texture IDs from Unity to WebGL texture objects. You can call WebGL functions on emscripten’s WebGL context, GLctx.

有关如何与 JavaScript 交互的更多信息，请参阅 emscripten 文档。

In addition, there are several plugins in the Unity installation folder that you can use as reference: PlaybackEngines/WebGLSupport/BuildTools/lib and PlaybackEngines/WebGLSupport/BuildTools/Emscripten/src/library*.

代码可见性

The recommended approach is to execute all the build code in its own scope. This allows you to embed your content on an arbitrary page without causing conflicts with the embedding page code, and lets you embed more than one build on the same page.

If you have all your JavaScript code in the form of .jslib plugins inside your project, then this JavaScript code will run inside the same scope as the compiled build and your code should work the same way as in previous versions of Unity. For example, the following objects and functions should be directly visible from the JavaScript plugin code: Module, SendMessage, HEAP8, ccall etc..

However, if you are planning to call the internal JavaScript functions from the global scope of the embedding page, you must use the unityInstance variable in your WebGL Template index.html. Do this after the Unity engine instantiation succeeds, for example:

  var myGameInstance = null;
    script.onload = () => {
      createUnityInstance(canvas, config, (progress) => {...}).then((unityInstance) => {
        myGameInstance = unityInstance;
        …

Then, you can send a message to the build using myGameInstance.SendMessage(), or access the build Module object using myGameInstance.Module.

从 JavaScript 调用 Unity 脚本函数

The recommended way of sending data or notification to the Unity script from the browser’s JavaScript is to call methods on GameObjects in your content. If you are making the call from a JavaScript plugin, embedded in your project, you can use the following code:

MyGameInstance.SendMessage(objectName, methodName, value);

其中，__objectName__ 是场景中的对象名称；__methodName__ 是当前附加到该对象的脚本中的方法名称；__value__ 可以是字符串、数字，也可为空。例如：

MyGameInstance.SendMessage('MyGameObject', 'MyFunction');
MyGameInstance.SendMessage('MyGameObject', 'MyFunction', 5);

MyGameInstance.SendMessage('MyGameObject', 'MyFunction', 'MyString');

If you would like to make a call from the global scope of the embedding page, see the Code Visibility section.

从 Unity 脚本调用 C 函数

Unity compiles your sources into JavaScript from C/C++ code using emscripten, so you can also write plugins in C/C++ code, and call these functions from C#. Therefore, instead of the .jslib file in the example above, you could have a C/C++ file in your project, which is automatically get compiled with your scripts, and you can call functions from it, just like in the JavaScript example above.

If you are using C++ (.cpp) to implement the plugin, then you must ensure the functions are declared with C linkage to avoid name mangling issues:

# include <stdio.h>

extern "C" void Hello ()
{
    printf("Hello, world!\n");
}

extern "C" int AddNumbers (int x, int y)
{
    return x + y;
}

Note: Unity is using the Emscripten version 2.0.19 toolchain.

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• replaced Pointer__stringify() with UTF8ToString in 2021.2 onwards

• 在 2020.1 中 unity.Instance 已替换为 createUnityInstance

• 修复了代码示例中的错误。

• 在 2019.1中，WebGL 实例 gameInstance 更名为 unityInstance