stdweb 0.2.0

A standard library for the client-side Web

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A standard library for the client-side Web


The goal of this crate is to provide Rust bindings to the Web APIs and to allow a high degree of interoperability between Rust and JavaScript.


You can directly embed JavaScript code into Rust:

let message = "Hello, 世界!";
let result = js! {
    alert( @{message} );
    return 2 + 2 * 2;

println!( "2 + 2 * 2 = {:?}", result );

Even closures are supported:

let print_hello = |name: String| {
    println!( "Hello, {}!", name );

js! {
    var print_hello = @{print_hello};
    print_hello( "Bob" );
    print_hello.drop(); // Necessary to clean up the closure on Rust's side.

You can also pass arbitrary structures thanks to serde:

struct Person {
    name: String,
    age: i32

js_serializable!( Person );

js! {
    var person = @{person};
    console.log( + " is " + person.age + " years old." );

This crate also exposes a number of Web APIs, for example:

let button = document().query_selector( "#hide-button" ).unwrap();
button.add_event_listener( move |_: ClickEvent| {
    for anchor in document().query_selector_all( "#main a" ) {
        js!( @{anchor}.style = "display: none;"; );

Design goals

  • Expose a full suite of Web APIs as exposed by web browsers.
  • Try to follow the original JavaScript conventions and structure as much as possible, except in cases where doing otherwise results in a clearly superior design.
  • Be a building block from which higher level frameworks and libraries can be built.
  • Make it convenient and easy to embed JavaScript code directly into Rust and to marshal data between the two.
  • Integrate with the wider Rust ecosystem, e.g. support marshaling of structs which implement serde's Serializable.
  • Put Rust in the driver's seat where a non-trivial Web application can be written without touching JavaScript at all.
  • Allow Rust to take part in the upcoming WebAssembly (re)volution.
  • Make it possible to trivially create standalone libraries which are easily callable from JavaScript.

Getting started

Take a look at some of the examples:

  • examples/minimal - a totally minimal example which calls alert
  • examples/todomvc - a naively implemented TodoMVC application; shows how to call into the DOM
  • examples/hasher - shows how to export Rust functions to JavaScript and how to call them from the browser or Nodejs

Running the examples

  1. Add one of Rust's Web targets with rustup.

    • For compiling to asmjs through Emscripten:

      $ rustup target add asmjs-unknown-emscripten
    • For compiling to WebAssembly through Emscripten:

      $ rustup target add wasm32-unknown-emscripten
    • For compiling to WebAssembly through Rust's native backend:

      $ rustup target add wasm32-unknown-unknown
  2. Install cargo-web:

    $ cargo install -f cargo-web
  3. Go into examples/todomvc and start the example.

    • For the asmjs-unknown-emscripten backend:

      $ cargo web start --target-asmjm-emscripten
    • For the wasm32-unknown-emscripten:

      $ cargo web start --target-webasm-emscripten
    • For the wasm32-unknown-unknown:

      $ cargo web start --target-webasm
  4. Visit http://localhost:8000 with your browser.

For the *-emscripten targets cargo-web is not neccessary, however the native wasm32-unknown-unknown which doesn't need Emscripten requires cargo-web to work!

Exposing Rust functions to JavaScript

WARNING: This is only supported for Rust's native wasm32-unknown-unknown target!

(Note: this is based on the examples/hasher example)

With the stdweb crate you can easily expose a Rust function to JavaScript like this:

extern crate stdweb;
extern crate sha1;

use sha1::Sha1;

fn hash( string: String ) -> String {
    let mut hasher = Sha1::new();
    hasher.update( string.as_bytes() );

fn main() {

    js! {
        Module.exports.sha1 = @{hash};

If you compile this code with cargo-web build --target-webasm you'll get two files:

  • target/wasm32-unknown-unknown/release/hasher.js
  • target/wasm32-unknown-unknown/release/hasher.wasm

You can copy them into your JavaScript project and load like any other JavaScript file:

<script src="hasher.js"></script>

After it's loaded you can access Rust.hasher, which is a Promise which will resolve once the WebAssembly module is loaded. Inside that promise you'll find the contents of Module.exports which we've set from our Rust code, which includes our exported function which you can now call:

    Rust.hasher.then( function( hasher ) {
        const string = "fiddlesticks";
        const hash = hasher.sha1( string );

        console.log( "Hash of " + string + " is '" + hash + "'" );

You can also use the very same hasher.js from Nodejs:

const hasher = require( "hasher.js" );

const string = "fiddlesticks";
const hash = hasher.sha1( string );

console.log( "Hash of " + string + " is '" + hash + "'" );

For the Nodejs environment the WebAssembly is compiled synchronously.


Licensed under either of

at your option.

Snippets of documentation which come from Mozilla Developer Network are covered under the CC-BY-SA, version 2.5 or later.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.