[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 <[email protected]>"] edition = "2018" [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.