dioxus/notes

🌗🚀 Dioxus

A concurrent, functional, virtual DOM for Rust

Resources

This overview provides a brief introduction to Dioxus. For a more in-depth guide, make sure to check out:

• Getting Started
• Book
• Reference
• Examples

Overview and Goals

Dioxus makes it easy to quickly build complex user interfaces with Rust. Any Dioxus app can run in the web browser, as a desktop app, as a mobile app, or anywhere else provided you build the right renderer.

Dioxus is heavily inspired by React, supporting many of the same concepts:

• Hooks for state
• VirtualDom & diffing
• Concurrency, fibers, and asynchronous rendering
• JSX-like templating syntax

If you know React, then you know Dioxus.

Dioxus is substantially more performant than many of the other Rust UI libraries (Yew/Percy) and is significantly more performant than React - roughly competitve with InfernoJS.

Remember: Dioxus is a library for declaring interactive user interfaces - it is not a dedicated renderer. Most 1st party renderers for Dioxus currently only support web technologies.

Brief Overview

All Dioxus apps are built by composing functions that take in a Scope which is generic over some Properties and return an Element. A Scope holds relevant state data for the the currently-rendered component.

To launch an app, we use the launch method for the specific renderer we want to use. In the launch function, we pass the app's Component.

use dioxus::prelude::*;

fn main() {
    dioxus::desktop::launch(app);
}

fn app(cx: Scope) -> Element {
    cx.render(rsx!("hello world!"))
}

Elements & your first component

To assemble UI trees with Dioxus, you need to use the render function on something called LazyNodes. To produce LazyNodes, you can use the rsx! macro or the NodeFactory API. For the most part, you want to use the rsx! macro.

Any element in rsx! can have attributes, listeners, and children. For consistency, we force all attributes and listeners to be listed before children.

let value = "123";

rsx!(
    div {
        class: "my-class {value}",                  // <--- attribute
        onclick: move |_| log::info!("clicked!"),   // <--- listener
        h1 { "hello world" },                       // <--- child
    }
)

The rsx! macro accepts attributes in "struct form" and will parse the rest of the body as child elements and rust expressions. Any rust expression that implements IntoIterator<Item = impl IntoVNode> will be parsed as a child.

rsx!(
    div {
        (0..10).map(|_| rsx!(span { "hello world" }))
    }
)

Used within components, the rsx! macro must be rendered into an Element with the render function on Scope.

If we want to omit the boilerplate of cx.render, we can simply pass in cx as the first argument of rsx. This is sometimes useful when we need to render nodes in match statements.

fn example(cx: Scope) -> Element {

    // both of these are equivalent
    cx.render(rsx!("hello world"))

    rsx!(cx, "hello world!")
}

Putting everything together, we can write a simple component that renders a list of elements:

fn app(cx: Scope) -> Element {
    let name = "dave";
    cx.render(rsx!(
        h1 { "Hello, {name}!" }
        div {
            class: "my-class",
            id: "my-id",

            (0..5).map(|i| rsx!(
                div { key: "{i}"
                    "FizzBuzz: {i}"
                }
            ))

        }
    ))
}

Components

We can compose these function components to build a complex app. Each new component we design must take some Properties. For components with no explicit properties, we can use the () type or simply omit the type altogether.

In Dioxus, all properties are memoized by default!

fn App(cx: Scope) -> Element {
    cx.render(rsx!(
        Header {
            title: "My App",
            color: "red",
        }
    ))
}

Our Header component takes a title and a color property, which we declare on an explicit HeaderProps struct.

// The `Props` derive macro lets us add additional functionality to how props are interpreted.
#[derive(Props, PartialEq)]
struct HeaderProps {
    title: String,
    color: String,
}

fn Header(cx: Scope<HeaderProps>) -> Element {
    cx.render(rsx!(
        div {
            background_color: "{cx.props.color}"
            h1 { "{cx.props.title}" }
        }
    ))
}

Components may use the inline_props macro to completely inline the props definition into the function arguments.

#[inline_props]
fn Header(cx: Scope, title: String, color: String) -> Element {
    cx.render(rsx!(
        div {
            background_color: "{color}"
            h1 { "{title}" }
        }
    ))
}

Components may also borrow data from their parent component. We just need to attach some lifetimes to the props struct.

Note: we don't need to derive PartialEq for borrowed props since they cannot be memoized.

#[derive(Props)]
struct HeaderProps<'a> {
    title: &'a str,
    color: &'a str,
}

fn Header<'a>(cx: Scope<'a, HeaderProps<'a>>) -> Element {
    cx.render(rsx!(
        div {
            background_color: "{cx.props.color}"
            h1 { "{cx.props.title}" }
        }
    ))
}

Components that begin with an uppercase letter may be called with the traditional (for React) curly-brace syntax like so:

rsx!(
    Header { title: "My App" }
)

Alternatively, if your components begin with a lowercase letter, you can use the function call syntax:

rsx!(
    header( title: "My App" )
)

Hooks

While components are reusable forms of UI elements, hooks are reusable forms of logic. Hooks provide us a way of retrieving state from the Scope and using it to render UI elements.

By convention, all hooks are functions that should start with use_. We can use hooks to define state and modify it from within listeners.

fn app(cx: Scope) -> Element {
    let name = use_state(&cx, || "world");

    rsx!(cx, "hello {name}!")
}

Hooks are sensitive to how they are used. To use hooks, you must abide by the "rules of hooks" (borrowed from react):

• Functions with "use_" should not be called in callbacks
• Functions with "use_" should not be called out of order
• Functions with "use_" should not be called in loops or conditionals

In a sense, hooks let us add a field of state to our component without declaring an explicit state struct. However, this means we need to "load" the struct in the right order. If that order is wrong, then the hook will pick the wrong state and panic.

Most hooks you'll write are simply composition of other hooks:

fn use_username(cx: &ScopeState, id: Uuid) -> bool {
    let users = use_context::<Users>(cx);
    users.get(&id).map(|user| user.logged_in).ok_or(false)
}

To create entirely new foundational hooks, we can use the use_hook method on ScopeState.

fn use_mut_string(cx: &ScopeState) -> &mut String {
    cx.use_hook(|_| "Hello".to_string())
}

If you want to extend Dioxus with some new functionality, you'll probably want to implement a new hook from scratch.

Putting it all together

Using components, templates, and hooks, we can build a simple app.

use dioxus::prelude::*;

fn main() {
    dioxus::desktop::launch(App);
}

fn App(cx: Scope) -> Element {
    let count = use_state(&cx, || 0);

    cx.render(rsx!(
        div { "Count: {count}" }
        button { onclick: move |_| count.set(count + 1), "Increment" }
        button { onclick: move |_| count.set(count - 1), "Decrement" }
    ))
}

Features

This overview doesn't cover everything. Make sure to check out the tutorial and reference guide on the official website for more details.

Beyond this overview, Dioxus supports:

• Server-side rendering
• Concurrent rendering (with async support)
• Web/Desktop/Mobile support
• Pre-rendering and rehydration
• Fragments, Portals, and Suspense
• Inline-styles
• Custom event handlers
• Custom elements
• Basic fine-grained reactivity (IE SolidJS/Svelte)
• and more!

Good luck!

Inspiration, Resources, Alternatives and Credits

Dioxus is inspired by:

• React: for its hooks, concurrency, suspense
• Dodrio: for its research in bump allocation, double buffering, and diffing architecture

Alternatives to Dioxus include:

• Yew: supports function components and web, but no SSR, borrowed data, or bump allocation. Rather slow at times.
• Percy: supports function components, web, ssr, but lacks state management
• Sycamore: supports function components, web, ssr, but closer to SolidJS than React
• MoonZoom/Seed: opinionated frameworks based on the Elm model (message, update) - no hooks

We've put a lot of work into making Dioxus ergonomic and familiar. Our target audience is TypeSrcipt developers looking to switch to Rust for the web - so we need to be comparabale to React.