Yew

Yew (pronounced /juː/, the same way as "you") is a modern Rust framework inspired by Elm and ReactJS 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.

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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:

src/main.rs

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

struct Model { }

enum Msg { DoIt, }

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
            true
        }
    }
}

}

impl Renderable for Model { fn view(&self) -> Html { html! { // Render your model here { "Click me!" } } } }

fn main() { yew::start_app::(); } ```

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.

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

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 context.rs for example):

```rust use yew::worker::*;

struct Worker { link: AgentLink, }

[derive(Serialize, Deserialize, Debug)]

pub enum Request { Question(String), }

[derive(Serialize, Deserialize, Debug)]

pub enum Response { Answer(String), }

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(_) => {
            self.link.response(who, 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:

```rust struct Model { context: Box>, }

enum Msg { ContextMsg(context::Response), }

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.

Components

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

rust html! { <nav class="menu"> <MyButton title="First Button" /> <MyButton title="Second Button "/> </nav> }

Scopes

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.

```rust // my_button.rs

[derive(Properties, PartialEq)]

pub struct Properties { pub hidden: bool, #[props(required)] pub color: Color, #[props(required)] pub onclick: Callback<()>, }

```

```rust // confirm_dialog.rs

html! {

Fragments

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

rust 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:

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

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.

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

Third-party crates and pure Rust expressions inside

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

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

impl Renderable for Model { fn view(&self) -> Html { html! {

{ Local::now() }

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

Services

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.

Implemented: * IntervalService * RenderService * TimeoutService * StorageService * DialogService * FetchService * WebSocketService

```rust use yew::services::{ConsoleService, TimeoutService};

struct Model { link: ComponentLink, console: ConsoleService, timeout: TimeoutService, }

impl Component for Model { fn update(&mut self, msg: Self::Message) -> ShouldRender { match msg { Msg::Fire => { let sendmsg = self.link.sendback(|| Msg::Timeout); self.timeout.spawn(Duration::fromsecs(5), send_msg); } Msg::Timeout => { self.console.log("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:

```rust pub struct CcxtService(Option);

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

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};
        console.log(ccxt.exchanges);
        return ccxt.exchanges;
    };
    let v: Vec<String> = v.try_into().expect("can't extract exchanges");
    v
}

// Wrap more methods here!

} ```

Easy-to-use data conversion and destructuring

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

Implemented: JSON, TOML, YAML, MSGPACK, CBOR.

In development: BSON, XML.

```rust use yew::format::Json;

[derive(Serialize, Deserialize)]

struct Client { firstname: String, lastname: String, }

struct Model { local_storage: StorageService, clients: Vec, }

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

toml [dependencies] yew = { git = "https://github.com/DenisKolodin/yew", 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:

bash cargo install cargo-web

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

Build

```bash cargo web build

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

cargo build --target wasm32-unknown-unknown ```

Running Tests

bash ./ci/run_tests.sh

Running the examples

There are many examples that show how the framework works: [counter], [crm], [customcomponents], [dashboard], [fragments], [gameoflife], [mountpoint], [npmandrest], [timer], [todomvc], [two_apps].

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

bash cargo web start

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

bash 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.