#spa #wasm #framework


A framework for single-page application in Rust

9 releases

0.0.9 Nov 20, 2022
0.0.8 Nov 19, 2022
0.0.7 Sep 29, 2022
0.0.5 May 23, 2022
0.0.2 Apr 17, 2020

#60 in WebAssembly

45 downloads per month

MPL-2.0 license

10K SLoC


Crates.io docs.rs Build

An incremental and fine-grained render frontend framework for Single Page Application in Rust.

This project is in its early stage, things are still missing and frequent breaking changes are expected.

Spair is both small and fast. Spair's performance is comparable to Leptos, Dominator, and Sycamore. See the benchmark here. Spair's app size is smaller than some others frameworks. See the comparision here.


  • Incremtental render
    • The render method creates the DOM tree on the first run, then updates it on subsequence runs.
  • Queue render for fine-grained render.
    • Must be enabled in Cargo.toml, like: spair = { version="x.y.z", features = ["queue-render"] }
    • (It is just a queue render, not using any kind of signals)
    • You have to wrap your values in spair::QrVal or spair::QrVec
    • Current version of queue render may not very efficient because each fine-grained-render need to borrow the component state separately by it own.
  • Component state can be accessed in every part of render code.
    • Spair's components tend to be big, Render is used for code splitting.
    • You can always access the component state in every Render without having to pass it around.
    • Component state can also be accessed from queue render, too.
  • (Almost) no macro is required for constructing DOM.
    • But Spair is quite verbose because of this.
    • (But a macro can be built on top of Spair).
    • spair::set_arm!() is the only macro you have to use, it saves your days, (without it, match_if is a nightmare to maintainers)
  • Routing
    • Just basic support, currently, you have to implement the routing logic by yourself.
  • async command
  • svg
  • Missing things here and there...
    • Errr, this is not a feature, obviously. I just put this here to remind potential users not to surprise about missing things :D.
    • For example, Spair currently just implements a handful number of events.

Not support (yet), do you want to contribute?

These features are extremely low (or even not) on my todo list.

  • #[derive(spair::Routes)]
  • Event delegation, under features = ["event-delegation"] if it is ever implemented.
    • But you can always do it manually
  • SSR (under a feature flag, too)
  • RSX macro (under a feature flag, too)

Cargo features

You can enabled a feature in your Cargo.toml like this: spair = { version="x.y.z", features = ["feature-name"] }

feature-name desciption
keyed-list Support keyed-list for incremental mode
svg Support svg element
queue-render Support fined-grained render (*)

(*) Lists render by queue-render are always keyed.

Run examples


  • Rust with wasm32-unknown-unknown target.
  • Trunk

In an example folder:

trunk serve

or, if it's slow, use: (especialy examples/boids or examples/game_of_life)

trunk serve --release

Open your browser at http://localhost:8080


Not yet. /examples/* is the best place to start now.

Sections below provide first looks into Spair.

Static-mode and update-mode

Spair works by iterating through every elements and attributes/properties in the current DOM, which is empty before the first render, creating new items or modifying existing items, it's the update-mode. But there are elements or attributes that will never change. You can tell Spair to just create them but ignore them when iterating over them later by turn on the static-mode.

items update-mode static-mode notes
attributes / properties default .static_attributes() call .static_attributes() after you are done with update-mode-attributes
elements default, .update_nodes() .static_nodes() only apply to elements (include .relement()), not apply to texts/renderable-items
texts / renderable-items .rupdate(value) .rstatic(value) not affected by mode introduced by .update_nodes() or .static_nodes()
  • .update_nodes() and .static_nodes() can be switched back and forth as many times as you want.
  • Again, please rememeber that .relement() is affected by .update_nodes() and .static_nodes().
    // default to update-mode attributes
    .value(&some_value) // will be checked and updated if changed
    .class_if("class-name", bool_value)
    .static_attributes() // we are done with update-mode attributes!
    .class("class-name") // class="class-name" is added on creation, but ignored on subsequence renders
    // just add child-elements, default to update mode.
    .p(|p| {}) // create and update a <p>
    .rupdate(value) // create and update a text
    .rstatic(value) // a create-only text - not affected by update-mode (default).
    .div(|d| {}) // a create-only <div> (because creating in static-mode)
    .rupdate(value) // an updatable text - not affected by `.static_nodes()`
    .rstatic(value) // a create-only text - because of `rstatic`, not cause by `static_nodes`

  • Important note: when an element is creating in static mode, all its content will be ignored (not update) after the first render.
    .static_nodes() // Elements append after this will be in static-mode
    .p(|p| {
        // This closure only execute once on the creation of <p>.
        // In the future update, this closure will be IGNORED,
        // therefore, all child-nodes of <p> will NOT be updated despite
        // being created in update-mode.
        p.span(|s| {})
            .rupdate(value); // NEW VALUE OF `value` WILL NEVER BE RENDERED.


Look in /examples for full examples

This is the render method of examples/counter:

impl spair::Component for State {
    type Routes = ();
    fn render(&self, element: spair::Element<Self>) {
        let comp = element.comp();
            .p(|p| {
                    .rstatic("The initial value is ")
            .rstatic(Button("-", comp.handler(State::decrement)))
            .rstatic(Button("+", comp.handler(State::increment)));

Render and StaticRender traits

You can split your codes into small pieces by implement Render or StaticRender on your data types and pass the values to .rupdate() or .rstatic() respectively.

Render and StaticRender are implemented for primitives (i8, ..., u64, f32, f64, bool, usize, isize). They are simply converted to strings and rendered as text nodes.

Access to the component state.

When implementing Render, StaticRender or ElementRender for your data types, you may want to access the state of your component:

impl spair::Render<State> for &YourType {
    fn render(self, nodes: spair::Nodes<State>) {
        let state = nodes.state(); // type of `state` is `&State`


Reconciliation? - No, you must use .match_if()

Spair does not do reconciliation, users must do it by themselves. When an expected element is not found, Spair create it, but if Spair found an element at the expected index, Spair just assume it is the expected element. Therefore, when you want to render different elements base on a condition, you must tell Spair to do that via .match_if().

The following code is extracted from examples/fetch/src/lib.rs:

    .match_if(|mi| match self.branch.as_ref() {
        Some(branch) => spair::set_arm!(mi) // `spair::set_arm!()` use `line!()` internally to set `render_on_arm_index()`
            // Render the content of `Some(branch)`
            // some code removed
        None => spair::set_arm!(mi)
            // There is no value: `None`? Then just render a button
            .button(|b| {/* some code removed */})


if some_condition {
    element.div(|d| {})
} else {
    element.p(|p| {})

Child components

Example: examples/components


Names conflict with Rust keywords

HTML's tags and attributes are implemented as methods in Spair. Names that are conflicted with Rust's keywords are implemented using raw identifers such as r#type, r#for...

Element and attribute/property with the same name.

There are elements named <span>, <label>... there are also attributes named span, label... and Spair implement all of them as methods. It's obviously not able to implement them on the same object. (Actually, Spair use traits for these, but conflicts are still there).

Therefore, to immediately add elements witch such names, call .update_nodes() or .static_nodes().

To set attributes/properties with such names, you have to call .attributes_only() or .static_attributes_only() first. After setting attributes/properties, you have to explicitly switch to nodes-mode using .update_nodes() or .static_nodes().


element.span(); // => Error

    .span(); // Element <span>  

    .span() // attribute
    .span(); // Element <span>  

Common errors

Using Spair, you may encounter common mistakes listed in this section. They are really annoying. How these problems can be avoided?

static_attributes(), static_nodes()

If you set attributes or add nodes in static-mode it will never be updated. It is easy to misplace an update-mode item under static-mode. For example, you have an app and have already converted all things that are you considered static to static-mode. Now, after a while, You decide to add something that you want it to be updated on change. But you placed it under a branch of the DOM tree without noticing that the branch is under static-mode. Finally, you give the new version of the app a test, at first, you may scratch head and check back and forth many times because it is renderd, but never update its value.


~171K SLoC