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Rust framework for building client web apps
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bors and jstarry Merge #589
589: Allow components to accept children elements r=jstarry a=jstarry

Fixes: #537

#### Terminology
- (B) Base component that renders components nested inside each other
- (P) Parent component that has a `children` property and can render those children
- (C) Child component that is nested inside parent and included inside the Parent's `children`

#### Todo
- [x] Add example for nested components
- [x] Support arbitrary html nested inside component tags
- [x] Support nested components inside component tags
- [x] Allow modifying & accessing (C) props when rendering (P)
- [x] Allow filtering (C) components when rendering (P)
- [x] Children prop be required or optional
- [x] Clean up nested component example
- [x] Fix parser for generic component type
- [x] Write tests
- [x] Update documentation and README
- [x] ~~Investigate passing required properties from (P) -> (C)~~
- [x] ~~Allow sending messages from (C) -> (B)~~

Co-authored-by: Justin Starry <>
Latest commit 24d39f9 Sep 10, 2019

Yew   Build Status

Rust / Wasm UI framework

Build Status Gitter Chat Rustc Version 1.35+

Examples | Changelog | Code of Conduct


Yew is a modern Rust framework inspired by Elm and React for creating multi-threaded frontend apps with WebAssembly.

The framework supports multi-threading & concurrency out of the box. It uses Web Workers API to spawn actors (agents) in separate threads and uses a local scheduler attached to a thread for concurrent tasks.

Become a sponsor on Patreon

Check out a live demo powered by yew-wasm-pack-template

Cutting Edge technologies

Rust to WASM compilation

This framework is designed to be compiled into modern browsers' runtimes: wasm, asm.js, emscripten.

To prepare the development environment use the installation instruction here: wasm-and-rust.

Clean MVC approach inspired by Elm and Redux

Yew implements strict application state management based on message passing and updates:


use yew::{html, Component, ComponentLink, Html, Renderable, ShouldRender};

struct Model { }

enum Msg {

impl Component for Model {
    // Some details omitted. Explore the examples to see more.

    type Message = Msg;
    type Properties = ();

    fn create(_: Self::Properties, _: ComponentLink<Self>) -> Self {
        Model { }

    fn update(&mut self, msg: Self::Message) -> ShouldRender {
        match msg {
            Msg::DoIt => {
                // Update your model on events

impl Renderable<Model> for Model {
    fn view(&self) -> Html<Self> {
        html! {
            // Render your model here
            <button onclick=|_| Msg::DoIt>{ "Click me!" }</button>

fn main() {

Predictable mutability and lifetimes (thanks Rust!) make it possible to reuse a single instance of the model without a need to create a fresh one on every update. It also helps to reduce memory allocations.

JSX-like templates with html! macro

Feel free to put pure Rust code into HTML tags with all the compiler and borrow checker's benefits.

html! {
    <section class="todoapp">
        <header class="header">
            <h1>{ "todos" }</h1>
            { view_input(&model) }
        <section class="main">
            <input class="toggle-all"
                   onclick=|_| Msg::ToggleAll />
            { view_entries(&model) }

Agents - actors model inspired by Erlang and Actix

Every Component can spawn an agent and attach to it. Agents are separate tasks that work concurrently.

Create your worker/agent (in for example):

use yew::worker::*;

struct Worker {
    link: AgentLink<Worker>,

#[derive(Serialize, Deserialize, Debug)]
pub enum Request {

#[derive(Serialize, Deserialize, Debug)]
pub enum Response {

impl Agent for Worker {
    // Available:
    // - `Job` (one per bridge)
    // - `Context` (shared in the same thread)
    // - `Public` (separate thread).
    type Reach = Context; // Spawn only one instance per thread (all components could reach this)
    type Message = Msg;
    type Input = Request;
    type Output = Response;

    // Create an instance with a link to agent's environment.
    fn create(link: AgentLink<Self>) -> Self {
        Worker { link }

    // Handle inner messages (of services of `send_back` callbacks)
    fn update(&mut self, msg: Self::Message) { /* ... */ }

    // Handle incoming messages from components of other agents.
    fn handle(&mut self, msg: Self::Input, who: HandlerId) {
        match msg {
            Request::Question(_) => {
      , Response::Answer("That's cool!".into()));

Build the bridge to an instance of this agent. It spawns a worker automatically or reuses an existing one, depending on the type of the agent:

struct Model {
    context: Box<Bridge<context::Worker>>,

enum Msg {

impl Component for Model {
    type Message = Msg;
    type Properties = ();

    fn create(_: Self::Properties, link: ComponentLink<Self>) -> Self {
        let callback = link.send_back(|_| Msg::ContextMsg);
        // `Worker::bridge` spawns an instance if no one is available
        let context = context::Worker::bridge(callback); // Connected! :tada:
        Model { context }

You can use as many agents as you want. For example you could separate all interactions with a server to a separate thread (a real OS thread because Web Workers map to the native threads).

REMEMBER! Not every API is available for every environment. For example you can't use StorageService from a separate thread. It won't work with Public agents, only with Job and Context ones.


Yew supports components! You could create a new one by implementing a Component trait and including it directly into the html! template:

html! {
    <nav class="menu">
        <MyButton title="First Button" />
        <MyButton title="Second Button "/>
        <MyList name="Grocery List">
          <MyListItem text="Apples" />


Components live in an Angular-like scopes with parent-to-child (properties) and child-to-parent (events) interaction.

Properties are also pure Rust types with strict type-checking during the compilation.


#[derive(Properties, PartialEq)]
pub struct Properties {
    pub hidden: bool,
    pub color: Color,
    pub onclick: Callback<()>,

html! {
    <div class="confirm-dialog">
        <MyButton onclick=|_| DialogMsg::Cancel color=Color::Red hidden=true />
        <MyButton onclick=|_| DialogMsg::Submit color=Color::Blue />


Yew supports fragments: elements without a parent which could be attached somewhere later.

html! {
        <tr><td>{ "Row" }</td></tr>
        <tr><td>{ "Row" }</td></tr>
        <tr><td>{ "Row" }</td></tr>

Virtual DOM, independent loops, fine updates

Yew uses its own virtual-dom implementation. It updates the browser's DOM with tiny patches when properties of elements have changed. Every component lives in its own independent loop interacting with the environment (Scope) through message passing and supports a fine control of rendering.

The ShouldRender returns the value which informs the loop when the component should be re-rendered:

fn update(&mut self, msg: Self::Message) -> ShouldRender {
    match msg {
        Msg::UpdateValue(value) => {
            self.value = value;
        Msg::Ignore => {

Using ShouldRender is more effective than comparing the model after every update because not every model change leads to a view update. It allows the framework to skip the model comparison checks entirely. This also allows you to control updates as precisely as possible.

Rust/JS/C-style comments in templates

Use single-line or multi-line Rust comments inside html-templates.

html! {
   /* Write some ideas
    * in multiline comments
    <p>{ "and tags can be placed between comments!" }</p>
    // <li>{ "or single-line comments" }</li>

Third-party crates and pure Rust expressions inside

Use external crates and put values from them into the template:

extern crate chrono;
use chrono::prelude::*;

impl Renderable<Model> for Model {
    fn view(&self) -> Html<Self> {
        html! {
            <p>{ Local::now() }</p>

Some crates don't support the true wasm target (wasm32-unknown-unknown) yet.


Yew has implemented pluggable services that allow you to call external APIs, such as: JavaScript alerts, timeout, storage, fetches and websockets. It's a handy alternative to subscriptions.


  • IntervalService
  • RenderService
  • TimeoutService
  • StorageService
  • DialogService
  • FetchService
  • WebSocketService
use yew::services::{ConsoleService, TimeoutService};

struct Model {
    link: ComponentLink<Model>,
    console: ConsoleService,
    timeout: TimeoutService,

impl Component for Model {
    fn update(&mut self, msg: Self::Message) -> ShouldRender {
        match msg {
            Msg::Fire => {
                let send_msg =|_| Msg::Timeout);
                self.timeout.spawn(Duration::from_secs(5), send_msg);
            Msg::Timeout => {

Can't find an essential service? Want to use a library from npm? You can reuse JavaScript libraries with stdweb capabilities and create your own service implementation. Here's an example below of how to wrap the ccxt library:

pub struct CcxtService(Option<Value>);

impl CcxtService {
    pub fn new() -> Self {
        let lib = js! {
            return ccxt;

    pub fn exchanges(&mut self) -> Vec<String> {
        let lib = self.0.as_ref().expect("ccxt library object lost");
        let v: Value = js! {
            var ccxt = @{lib};
            return ccxt.exchanges;
        let v: Vec<String> = v.try_into().expect("can't extract exchanges");

    // Wrap more methods here!

Easy-to-use data conversion and destructuring

Yew allows for serialization (store/send and restore/receive) formats.


In development: BSON, XML.

use yew::format::Json;

#[derive(Serialize, Deserialize)]
struct Client {
    first_name: String,
    last_name: String,

struct Model {
    local_storage: StorageService,
    clients: Vec<Client>,

impl Component for Model {
    fn update(&mut self, msg: Self::Message) -> ShouldRender {
        Msg::Store => {
            // Stores it, but in JSON format/layout
  , Json(&model.clients));
        Msg::Restore => {
            // Tries to read and destructure it as JSON formatted data
            if let Json(Ok(clients)) = self.local_storage.restore(KEY) {
                model.clients = clients;

Only JSON is available by default but you can activate the rest through features in your project's Cargo.toml:

yew = { git = "", features = ["toml", "yaml", "msgpack", "cbor"] }

Development setup

Clone or download this repository.

Install cargo-web

This is an optional tool that simplifies deploying web applications:

cargo install cargo-web

Add --force option to ensure you install the latest version.


cargo web build

# without cargo-web, only the wasm32-unknown-unknown target is supported
cargo build --target wasm32-unknown-unknown

Running Tests


Running the examples

There are many examples that show how the framework works: counter, crm, custom_components, dashboard, fragments, game_of_life, mount_point, npm_and_rest, timer, todomvc, two_apps.

To start an example enter its directory and start it with cargo-web:

cargo web start

To run an optimised build instead of a debug build use:

cargo web start --release

This will use the wasm32-unknown-unknown target by default, which is Rust's native WebAssembly target. The Emscripten-based wasm32-unknown-emscripten and asmjs-unknown-emscripten targets are also supported if you tell the cargo-web to build for them using the --target parameter.

Project templates

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