leptos/README.md

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You can find a list of useful libraries and example projects at awesome-leptos.

Leptos

use leptos::*;

#[component]
pub fn SimpleCounter(initial_value: i32) -> impl IntoView {
    // create a reactive signal with the initial value
    let (value, set_value) = create_signal(initial_value);

    // create event handlers for our buttons
    // note that `value` and `set_value` are `Copy`, so it's super easy to move them into closures
    let clear = move |_| set_value(0);
    let decrement = move |_| set_value.update(|value| *value -= 1);
    let increment = move |_| set_value.update(|value| *value += 1);

    // create user interfaces with the declarative `view!` macro
    view! {
        <div>
            <button on:click=clear>Clear</button>
            <button on:click=decrement>-1</button>
            // text nodes can be quoted or unquoted
            <span>"Value: " {value} "!"</span>
            <button on:click=increment>+1</button>
        </div>
    }
}

// Easy to use with Trunk (trunkrs.dev) or with a simple wasm-bindgen setup
pub fn main() {
    mount_to_body(|| view! {
        <SimpleCounter initial_value=3 />
    })
}

About the Framework

Leptos is a full-stack, isomorphic Rust web framework leveraging fine-grained reactivity to build declarative user interfaces.

What does that mean?

• Full-stack: Leptos can be used to build apps that run in the browser (client-side rendering), on the server (server-side rendering), or by rendering HTML on the server and then adding interactivity in the browser (server-side rendering with hydration). This includes support for HTTP streaming of both data (Resources) and HTML (out-of-order or in-order streaming of <Suspense/> components.)
• Isomorphic: Leptos provides primitives to write isomorphic server functions, i.e., functions that can be called with the “same shape” on the client or server, but only run on the server. This means you can write your server-only logic (database requests, authentication etc.) alongside the client-side components that will consume it, and call server functions as if they were running in the browser, without needing to create and maintain a separate REST or other API.
• Web: Leptos is built on the Web platform and Web standards. The router is designed to use Web fundamentals (like links and forms) and build on top of them rather than trying to replace them.
• Framework: Leptos provides most of what you need to build a modern web app: a reactive system, templating library, and a router that works on both the server and client side.
• Fine-grained reactivity: The entire framework is built from reactive primitives. This allows for extremely performant code with minimal overhead: when a reactive signal’s value changes, it can update a single text node, toggle a single class, or remove an element from the DOM without any other code running. (So, no virtual DOM overhead!)
• Declarative: Tell Leptos how you want the page to look, and let the framework tell the browser how to do it.

Learn more

Here are some resources for learning more about Leptos:

• Book (work in progress)
• Examples
• API Documentation
• Common Bugs (and how to fix them!)

nightly Note

Most of the examples assume you’re using nightly version of Rust and the nightly feature of Leptos. To use nightly Rust, you can either set your toolchain globally or on per-project basis.

To set nightly as a default toolchain for all projects (and add the ability to compile Rust to WebAssembly, if you haven’t already):

rustup toolchain install nightly
rustup default nightly
rustup target add wasm32-unknown-unknown

If you'd like to use nightly only in your Leptos project however, add rust-toolchain.toml file with the following content:

[toolchain]
channel = "nightly"
targets = ["wasm32-unknown-unknown"]

The nightly feature enables the function call syntax for accessing and setting signals, as opposed to .get() and .set(). This leads to a consistent mental model in which accessing a reactive value of any kind (a signal, memo, or derived signal) is always represented as a function call. This is only possible with nightly Rust and the nightly feature.

cargo-leptos

cargo-leptos is a build tool that's designed to make it easy to build apps that run on both the client and the server, with seamless integration. The best way to get started with a real Leptos project right now is to use cargo-leptos and our starter templates for Actix or Axum.

cargo install cargo-leptos
cargo leptos new --git https://github.com/leptos-rs/start
cd [your project name]
cargo leptos watch

Open browser to http://localhost:3000/.

FAQs

What’s up with the name?

Leptos (λεπτός) is an ancient Greek word meaning “thin, light, refined, fine-grained.” To me, a classicist and not a dog owner, it evokes the lightweight reactive system that powers the framework. I've since learned the same word is at the root of the medical term “leptospirosis,” a blood infection that affects humans and animals... My bad. No dogs were harmed in the creation of this framework.

Is it production ready?

People usually mean one of three things by this question.

1. Are the APIs stable? i.e., will I have to rewrite my whole app from Leptos 0.1 to 0.2 to 0.3 to 0.4, or can I write it now and benefit from new features and updates as new versions come?

The APIs are basically settled. We’re adding new features, but we’re very happy with where the type system and patterns have landed. I would not expect major breaking changes to your code to adapt to future releases, in terms of architecture.

2. Are there bugs?

Yes, I’m sure there are. You can see from the state of our issue tracker over time that there aren’t that many bugs and they’re usually resolved pretty quickly. But for sure, there may be moments where you encounter something that requires a fix at the framework level, which may not be immediately resolved.

3. Am I a consumer or a contributor?

This may be the big one: “production ready” implies a certain orientation to a library: that you can basically use it, without any special knowledge of its internals or ability to contribute. Everyone has this at some level in their stack: for example I (@gbj) don’t have the capacity or knowledge to contribute to something like wasm-bindgen at this point: I simply rely on it to work.

There are several people in the community using Leptos right now for internal apps at work, who have also become significant contributors. I think this is the right level of production use for now. There may be missing features that you need, and you may end up building them! But for internal apps, if you’re willing to build and contribute missing pieces along the way, the framework is definitely usable right now.

Can I use this for native GUI?

Sure! Obviously the view macro is for generating DOM nodes but you can use the reactive system to drive native any GUI toolkit that uses the same kind of object-oriented, event-callback-based framework as the DOM pretty easily. The principles are the same:

• Use signals, derived signals, and memos to create your reactive system
• Create GUI widgets
• Use event listeners to update signals
• Create effects to update the UI

I've put together a very simple GTK example so you can see what I mean.

The new rendering approach being developed for 0.7 supports “universal rendering,” i.e., it can use any rendering library that supports a small set of 6-8 functions. (This is intended as a layer over typical retained-mode, OOP-style GUI toolkits like the DOM, GTK, etc.) That future rendering work will allow creating native UI in a way that is much more similar to the declarative approach used by the web framework.