WebAssembly (WASM) for High Performance Apps · Pelajaran

Callback JavaScript Khusus

Rancang dan implementasikan fungsi JavaScript khusus yang dapat dipanggil dari dalam modul WebAssembly Anda.

Pelajaran 2 dari 412 langkah

Callback JavaScript Khusus adalah pelajaran WebAssembly (WASM) for High Performance Apps gratis di CoddyKit. Ini adalah pelajaran 2 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar WebAssembly (WASM) for High Performance Apps, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus WebAssembly (WASM) for High Performance Apps mencakup 4 pelajaran total.

Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.

Calling JavaScript from WASM

Sometimes, your WebAssembly (WASM) module needs to communicate back to the JavaScript environment it's running in. This is where custom JavaScript callbacks become essential!

They allow your WASM code to trigger actions or pass data back to your web page, making your applications more interactive.

Why WASM Needs Callbacks

Imagine your WASM module performs complex calculations or processes data. Once it's done, it often needs to:

Update the UI: Notify JavaScript to refresh a chart or display a result.
Access Browser APIs: Request JavaScript to use APIs WASM can't directly access, like `localStorage` or `fetch`.
Log Information: Send debugging messages or status updates to the browser console.
Handle Events: Respond to user interactions or system events managed by JavaScript.

JavaScript Provides the Function

From the JavaScript side, setting up a callback is straightforward. You simply define a regular JavaScript function. This function will then be made available to your WebAssembly module during its initialization.

Think of it as giving your WASM module a direct line to call back into your JavaScript application when needed.

WASM Declares the Import

On the WebAssembly side (e.g., in Rust or C/C++), you need to declare that your module expects to import a function from its host environment (JavaScript).

In Rust, you use the #[wasm_bindgen] attribute with an extern "C" block.
This declaration specifies the function's name and its expected signature (parameters and return type).
It tells the WASM compiler that this function call will be resolved externally by JavaScript.

Rust Code: Importing JavaScript

Let's look at a Rust example. We'll import a JavaScript function named logMessageFromWasm. When Rust calls this, the corresponding JS function will execute.

/* lib.rs */
use wasm_bindgen::prelude::*;

#[wasm_bindgen]
extern "C" {
    // Imports a JS function named 'logMessageFromWasm'
    // It takes a string and returns nothing.
    #[wasm_bindgen(js_name = logMessageFromWasm)]
    fn log_message_from_wasm(s: &str);
}

#[wasm_bindgen]
pub fn call_js_log() {
    log_message_from_wasm("Hello from Rust!");
}

Running the Callback (JS + Rust)

To run the Rust code from the previous scene, we compile it to a .wasm module and use wasm-bindgen's glue code. Then, we define our JavaScript callback and load the WASM.

Check your browser's developer console after running!

<!-- index.html -->
<!DOCTYPE html>
<html>
<head>
    <title>WASM Callback Demo</title>
</head>
<body>
    <h1>Check console for WASM message!</h1>
    <script type="module">
        // Assuming 'pkg/rust_wasm_module.js' is generated by wasm-pack
        import init, { call_js_log } from './pkg/rust_wasm_module.js';

        // Define the JavaScript function that WASM will call
        window.logMessageFromWasm = (message) => {
            console.log("JS received:", message);
        };

        async function run() {
            await init(); // Initialize the WASM module
            call_js_log(); // Call the Rust function, which calls JS
        }

        run();
    </script>
</body>
</html>

Passing Data to Callbacks

Callbacks are not just for simple notifications; they can also pass data from your WebAssembly module back to JavaScript. This is crucial for returning results or providing context.

Primitive Types: Numbers (integers, floats) and booleans are passed directly.
Strings: With wasm-bindgen, Rust strings (`&str`) are efficiently converted to JavaScript strings.
Complex Objects: For more intricate data structures, `wasm-bindgen` provides mechanisms for seamless serialization and deserialization.

Callback with Arguments (Rust)

Let's enhance our Rust example to pass a number back to JavaScript. The `log_number_from_wasm` function is imported, expecting an integer argument.

Our Rust function `calculate_and_log` will perform a sum and then pass the result to this JS callback.

/* lib.rs */
use wasm_bindgen::prelude::*;

#[wasm_bindgen]
extern "C" {
    // Imports a JS function that takes an i32 number
    #[wasm_bindgen(js_name = logNumberFromWasm)]
    fn log_number_from_wasm(num: i32);
}

#[wasm_bindgen]
pub fn calculate_and_log(a: i32, b: i32) {
    let result = a + b;
    log_number_from_wasm(result); // Call JS with the calculated result
}

Running Callback with Arguments

Here's the JavaScript setup for the previous Rust example. Notice how the `window.logNumberFromWasm` function now accepts a numeric argument, which it then prints to the console.

<!-- index.html -->
<!DOCTYPE html>
<html>
<head>
    <title>WASM Callback Args Demo</title>
</head>
<body>
    <h1>Check console for calculated result!</h1>
    <script type="module">
        import init, { calculate_and_log } from './pkg/rust_wasm_module.js';

        // This JS function will receive a number from WASM
        window.logNumberFromWasm = (number) => {
            console.log("JS received result:", number);
        };

        async function run() {
            await init();
            calculate_and_log(10, 20); // Call Rust with arguments 10 and 20
        }

        run();
    </script>
</body>
</html>

Common Callback Scenarios

Custom callbacks are incredibly versatile and enable WASM to integrate smoothly with the browser's environment. Some common use cases include:

User Interface Updates: Notifying JS to update elements after a WASM computation is complete.
Browser API Access: Requesting JS to use `localStorage`, `fetch`, or directly manipulate the DOM.
Event Handling: Allowing WASM to react to user input or browser events processed by JS.
Logging and Debugging: Sending detailed messages to the browser console from within WASM for monitoring.

Quick Check on Callbacks

Understanding how to declare and use imported functions is key to effective WASM-JS communication.

Jawab di pelajaran interaktif

Recap: Custom JS Callbacks

You've learned how to enable your WebAssembly modules to call back into JavaScript!

WASM modules can import and call JavaScript functions.
wasm-bindgen simplifies this process in Rust, allowing type-safe data exchange.
Callbacks are crucial for UI updates, accessing browser APIs, and logging from WASM.

This powerful pattern makes WASM applications more dynamic and integrated with the web environment. Keep experimenting!

Gratis untuk memulai

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Tulis dan jalankan kode asli di browser kamu, dapatkan bantuan instan dari tutor AI 24/7, dan lanjutkan di mana kamu tinggalkan di web atau aplikasi.

Kursus: 12
Pelajaran: 48

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Pertanyaan yang Sering Diajukan

Apakah pelajaran “Callback JavaScript Khusus” gratis?

Ya — teks lengkap “Callback JavaScript Khusus” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus WebAssembly (WASM) for High Performance Apps, upgrade ke CoddyKit PRO. Kursus WebAssembly (WASM) for High Performance Apps mencakup 4 pelajaran total.

Apa yang akan aku pelajari di “Callback JavaScript Khusus”?

Rancang dan implementasikan fungsi JavaScript khusus yang dapat dipanggil dari dalam modul WebAssembly Anda. Kamu berlatih WebAssembly (WASM) for High Performance Apps dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.

Apakah aku perlu pengalaman untuk memulai WebAssembly (WASM) for High Performance Apps?

Tidak diperlukan pengalaman sebelumnya. WebAssembly (WASM) for High Performance Apps di CoddyKit dirancang untuk pemula hingga pelajar tingkat lanjut, jadi kamu bisa memulai di sini atau dari awal dan belajar sesuai kecepatan kamu sendiri. Ini adalah pelajaran 2 dari 4.

Berapa lama pelajaran “Callback JavaScript Khusus” memakan waktu?

Sebagian besar pelajaran CoddyKit memakan waktu sekitar 5–10 menit. Setiap pelajaran ringkas dan interaktif, jadi kamu membuat kemajuan stabil dan melanjutkan dari tempat kamu tinggalkan di web dan aplikasi.

Bisakah aku menulis dan menjalankan kode dalam pelajaran WebAssembly (WASM) for High Performance Apps ini?

Ya. Setiap pelajaran WebAssembly (WASM) for High Performance Apps menyertakan editor kode bawaan, jadi kamu menulis dan menjalankan kode nyata langsung di browser dan mendapatkan umpan balik AI instan — tidak diperlukan penyiapan lokal.

Semua pelajaran dalam kursus ini

Operasi Asinkron dengan WASM
Callback JavaScript Khusus
Penanganan Kesalahan & Eksepsi
Berbagi Memori dan Larik Bertipe di Seluruh Batas JS/WASM

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