تحميل WASM وتشغيله في JavaScript

Welcome! You've learned how to compile C/C++ code into a .wasm file. Now, it's time to bring that powerful WebAssembly module to life in your web browser.

This lesson will guide you through loading your .wasm module using JavaScript and invoking its functions.

Modern web browsers provide a global WebAssembly object. This object is your primary interface for interacting with WebAssembly modules.

• It allows you to compile, instantiate, and manage WASM code.
• We'll use its methods to fetch and load our .wasm file into the browser's runtime.

The most efficient way to load a WASM module from a network request is using WebAssembly.instantiateStreaming().

• It directly streams the raw bytes from the network response.
• It compiles and instantiates the module in one go, saving time and resources.
• This method expects a Response object, typically obtained from the fetch() API.

Let's assume we have a very basic C function that adds two numbers, like this one. This function will be compiled into add.wasm (as covered in the previous lesson) and then exported from the WASM module.

This export makes it callable directly from JavaScript.

Before we can instantiate our WASM module, we need to fetch the .wasm file itself. The standard fetch() API is perfect for this task.

It returns a Promise that resolves to a Response object, which we'll then pass to instantiateStreaming().

The WebAssembly.instantiateStreaming() function takes the Response and returns a Promise. This Promise resolves to an object containing two important properties:

• module: The compiled WebAssembly module itself.
• instance: An object representing the running instance of the module, which holds its exports.

Once you have the instance object, you can access any functions or global variables that were exported from your WASM module. These are available through its exports property.

For our C add function, when compiled to WASM and exported, it will be accessible in JavaScript as instance.exports.add.

Here's a complete JavaScript code snippet. It fetches add.wasm, instantiates it, and then calls the exported add function with two numbers, logging the result.

This code would run inside a <script> tag in an HTML file.

The instance object is your primary interface to the running WebAssembly module. It contains more than just exported functions:

• instance.exports: An object holding all functions, globals, and memory exported by the WASM module.
• instance.module: A reference to the compiled WebAssembly.Module object.
• instance.memory: If the WASM module uses memory, this provides access to its linear memory (an ArrayBuffer).

You've seen how to efficiently load and instantiate a WASM module. What is the key JavaScript function used for this purpose when streaming from a network request?

Fantastic work! You've successfully learned how to bring your compiled WebAssembly modules to life in the browser. Here's what we covered:

• Using the global WebAssembly object.
• Efficiently loading with WebAssembly.instantiateStreaming().
• Accessing exported functions via the instance.exports object.
• Calling WASM functions directly from JavaScript.

Now you can execute high-performance code right in your web applications!