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Smithy is a front-end framework for Rust

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What is Smithy?

Smithy is a framework for writing WebAssembly applications entirely in Rust. Its goal is to allow you to do so using idiomatic Rust, without giving up any of the compiler's safety guarantees.

Smithy works on nightly

Smithy v0.0.7 currently works on 1.39.0-nightly (dfd43f0fd 2019-09-01).

Getting started

Getting started in Smithy is easy!

npm init smithy-app my_smithy_app
cd my_smithy_app
npm start

Navigate to localhost:8080 to see your app in action!

See the create-smithy-app repository for more details.

A simple Smithy app

A simple click counter is as follows:

pub fn start() -> Result<(), wasm_bindgen::JsValue> {
  let root_element = get_root_element()?;
  let mut count = 0;
  let app = smithy::smd!(
    <div on_click={|_| count = count + 1}>
      I have been clicked {count}{' '}times.
  smithy::mount(Box::new(app), root_element);

fn get_root_element() -> Result<web_sys::Element, wasm_bindgen::JsValue> {
  let document = web_sys::window().unwrap().document().unwrap();

How Smithy works

smd! macro

The smd! and smd_borrowed! macros convert something that looks like JSX into a wrapper around an FnMut(smithy::types::Phase) -> smithy::types::PhaseResult. For example, the smd! call in:

let mut count = 0;
let app = smithy::smd!(
  <div on_click={|_| count = count + 1}>
    I have been clicked {count}{' '}times.

is converted into

let mut app = {
  use smithy::types::Component;
  let component: smithy::types::SmithyComponent =
    smithy::types::SmithyComponent(Box::new(move |phase| match phase {
      smithy::types::Phase::Rendering => {
          smithy::types::Node::Dom(smithy::types::HtmlToken {
            node_type: "div".into(),
            attributes: std::collections::HashMap::new(),
            children: {
              let mut children = Vec::with_capacity(4usize);
              children.push(smithy::types::Node::Text("I have been clicked ".into()));
              children.push({ count }.render());
              children.push({ ' ' }.render());
      smithy::types::Phase::UiEventHandling(ui_event_handling) => match ui_event_handling {
        (evt, [0usize, 1usize, rest @ ..]) => {
          smithy::types::PhaseResult::UiEventHandling({ count }.handle_ui_event(evt, rest))
        (evt, [0usize, 2usize, rest @ ..]) => {
          smithy::types::PhaseResult::UiEventHandling({ ' ' }.handle_ui_event(evt, rest))
        (smithy::types::UiEvent::OnClick(val), [0usize, rest @ ..]) => {
          ({ |_| count = count + 1 })(val);
        _ => smithy::types::PhaseResult::UiEventHandling(false),
      smithy::types::Phase::WindowEventHandling(window_event) => {
        let mut event_handled = false;
        event_handled = ({ count }).handle_window_event(window_event) || event_handled;
        event_handled = ({ ' ' }).handle_window_event(window_event) || event_handled;
        match window_event {
          _ => smithy::types::PhaseResult::WindowEventHandling(event_handled),
      smithy::types::Phase::PostRendering => {
            ({ count }).handle_post_render();
          ({ ' ' }).handle_post_render();
      smithy::types::Phase::RefAssignment(path_so_far) => {
        let new_path = path_so_far
          .chain(vec![0usize, 1usize])
        ({ count }).handle_ref_assignment(new_path);
        let new_path = path_so_far
          .chain(vec![0usize, 2usize])
        ({ ' ' }).handle_ref_assignment(new_path);

Notice that the |_| count = count + 1 and {count} are in separate branches of the match arm. If they had not been (e.g. if smd! created a struct instead of an FnMut), this would not have compiled. The borrow checker would have complained that you cannot immutably borrow count, as it is already borrowed mutably in the on_click callback.

Smithy phases

As you can see from the expansion of the smd! macro above, phases are a core concept in Smithy. In particular, an app is driven through five phases:

  • rendering, in which the app is asked to return a struct containing the information about what it will write to the DOM.
  • ref assignment, in which any app with ref={&mut optional_web_sys_html_element} will have Some(some_html_element) assigned to that ref.
  • post rendering, in which any post_render={|_| ...} callbacks will be executed. These callbacks are guaranteed to have all refs already assigned, thus allowing you to do any direct DOM manipulation you need to do.
  • UI event handling and window event handling, in which Smithy executes callbacks in response to events. After a callback is executed, Smithy will re-run the app through the different phases.
    • (UI event handling and window event handling are treated as separate phases, though conceptually they are very similar.)

smd! vs smd_borrowed!

As you can see in the macro expansion above, the smd! macro creates a move closure. This is not always desirable. If you do not wish to create a move closure, use smd_borrowed! instead.

How to get involved

Smithy is always looking for contributors! Please tweet at me @statisticsftw or take a look at the Smithy roadmap.

In addition, please take Smithy out for a spin using create-smithy-app.

Thanks! Happy coding!