Unity Javascript Bridge Integration

Unity JavaScript Bridge Integration

This skill governs the secure memory marshaling and bridging between Unity's C# WebAssembly environment and the native browser JavaScript DOM via .jslib plugins.

When to Use

• Use when calling browser window APIs from Unity C# (e.g., MRAID open()).
• Use when passing data (strings, arrays) from JS into Unity SendMessage.
• NOT for standard Unity game logic.

Core Process

Phase 1: JSLIB Definition

• Create .jslib files in the Assets/Plugins/WebGL directory.
• Wrap all functions in mergeInto(LibraryManager.library, { ... });.

Phase 2: Memory Marshaling (Strings)

WebAssembly uses a linear memory model. Passing strings requires explicit memory allocation.

• C# to JS: C# strings are passed as memory pointers. You must use UTF8ToString(ptr) on the JS side to read them.
• JS to C#: Returning a string from JS to C# requires allocating memory in the Wasm heap using _malloc, writing the string via stringToUTF8, and returning the pointer.

Phase 3: P/Invoke Architecture

• Define the external functions in C# using [DllImport("__Internal")].
• Do not call these functions if Application.platform != RuntimePlatform.WebGLPlayer. It will crash the editor.

Common Rationalizations

Red Flags

• Returning raw JS strings from .jslib functions instead of _malloc pointers.
• Failing to call _free on the C# side after receiving an allocated string pointer from JS.

Verification

Before finalizing the JS bridge, verify:

• All [DllImport] calls are wrapped in WebGL platform checks.
• Strings returned from JS are allocated via _malloc.
• C# code safely handles or frees memory pointers received from the bridge.