[Rust] Load a WebAssembly Function Written in Rust and Invoke it from JavaScript
In this lesson we are going to setup a project from scratch by introducing the JavaScript snippet to load a WebAssembly module. We demonstrate two different ways and showcase the benefit of the streaming solution. Once the module is loaded we can invoke a function previously exported from our Rust code.
Create a new project as a library:
cargo new --lib utils
Go to the project folder, modify Cargo.toml:
[package]
name = "utils"
version = "0.1.0"
authors = ["zhentian-wan <answer881215@gmail.com>"]
edition = "" [dependencies] [lib]
crate-type = ["cdylib"]
Create an function in src/lib.rs:
#[no_mangle]
pub extern fn add_one(x: u32) -> u32 {
x + 1
}
The extern keyword is needed to create an interface, so that this function can be invoked from other languages. The function accepts a value x, which is an unsigned integer, which is incremented by one and returned. In addition, we need to add a no-mangle annotation to tell the Rust compiler not to mangle the name of this function.
Run:
cargo build --target wasm32-unknown-unknown --release
wasm-gc target/wasm32-unknown-unknown/release/utils.wasm -o utils.gc.wasm
Create an index.html file and load utils.gc.wasm file we just generated:
<!DOCTYPE html>
<html>
<head>
<script>
WebAssembly.instantiateStreaming(fetch("utils.gc.wasm"))
.then(wasmModule => {
const result = wasmModeult.instance.exports.add_one(3);
const text = document.createTextNode(result);
document.body.appendChild(text);
});
</script>
<head>
<body></body>
<html>
Run:
http
Open the broswer we should see the output 4.
Be aware, instantiate streaming requires that our WASM file must be served with a content type, application/wasm. Fortunately, our HTTP server already does so.
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