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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