12 releases (breaking)
0.9.0 | May 26, 2023 |
---|---|
0.7.1 | Apr 18, 2023 |
0.6.0 | Mar 28, 2023 |
0.4.0 | Jun 30, 2022 |
0.1.0 | Aug 8, 2021 |
#1318 in WebAssembly
Used in 2 crates
(via kobold)
125KB
3K
SLoC
Kobold
Easy declarative web interfaces.
Key features:
- Declarative
view!
macro that uses HTML-esque syntax complete with optional closing tags. - Functional components with optional parameters.
- State management and event handling.
- High performance and consistently the lowest Wasm footprint in the Rust ecosystem.
Zero-Cost Static HTML
The view!
macro produces opaque impl View
types that by default do no allocations.
All static DOM elements compile to
inline JavaScript code that constructs them. Expressions are injected into the constructed DOM on first render.
Kobold keeps track of the DOM node references for these expressions.
Since the exact types the expressions evaluate to are known to the Rust compiler, update calls can diff them by
value (or pointer) and surgically update the DOM should they change. Changing a
string or an integer only updates the exact Text
node
that string or integer was rendered to.
If the view!
macro invocation contains DOM elements with no expressions, the constructed View
type will be zero-sized, and its View::update
method will be empty, making updates of static
DOM literally zero-cost.
Hello World!
Components in Kobold are created by annotating a render function with a #[component]
attribute.
use kobold::prelude::*;
#[component]
fn Hello(name: &str) -> impl View + '_ {
view! {
<h1>"Hello "{ name }"!"</h1>
}
}
fn main() {
kobold::start(view! {
<Hello name="Kobold" />
});
}
The component function must return a type that implements the View
trait. Since the view!
macro
produces transient locally defined types the best approach here is to always use the opaque impl View
return type.
Everything here is statically typed and the macro doesn't delete any information when manipulating the token stream, so the Rust compiler can tell you when you've made a mistake:
error[E0560]: struct `Hello` has no field named `nam`
--> examples/hello_world/src/main.rs:12:16
|
12 | <Hello nam="Kobold" />
| ^^^ help: a field with a similar name exists: `name`
You can even use rust-analyzer to refactor component or field names, and it will change the invocations inside the macros for you.
State management
The stateful
function can be used to create views that own and manipulate
their state:
use kobold::prelude::*;
#[component]
fn Counter(init: u32) -> impl View {
stateful(init, |count| {
bind! { count:
// Create an event handler with access to `&mut u32`
let onclick = move |_event| *count += 1;
}
view! {
<p>
"You clicked the "
// `{onclick}` here is shorthand for `onclick={onclick}`
<button {onclick}>"Button"</button>
" "{ count }" times."
</p>
}
})
}
fn main() {
kobold::start(view! {
<Counter init={0} />
});
}
The stateful
function takes two parameters:
- State constructor that implements the
IntoState
trait. Kobold comes with default implementations for most primitive types, so we can useu32
here. - The anonymous render function that uses the constructed state, in our case its argument is
&Hook<u32>
.
The Hook
here is a smart pointer to the state itself that allows non-mutable access to the
state. The bind!
macro can be invoked for any Hook
to create closures with &mut
references to the
underlying state.
For more details visit the stateful
module documentation.
Optional parameters
Use #[component(<param>?)]
syntax to set a component parameter as default:
// `code` will default to `200` if omitted
#[component(code?: 200)]
fn Status(code: u32) -> impl View {
view! {
<p> "Status code was "{ code }
}
}
view! {
// Status code was 200
<Status />
// Status code was 404
<Status code={404} />
}
For more details visit the #[component]
macro documentation.
Conditional Rendering
Because the view!
macro produces unique transient types, if
and match
expressions that invoke
the macro will naturally fail to compile.
Using the auto_branch
flag on the #[component]
attribute
Kobold will scan the body of of your component render function, and make all view!
macro invocations
inside an if
or match
expression, and wrap them in an enum making them the same type:
#[component(auto_branch)]
fn Conditional(illuminatus: bool) -> impl View {
if illuminatus {
view! { <p> "It was the year when they finally immanentized the Eschaton." }
} else {
view! { <blockquote> "It was love at first sight." }
}
}
For more details visit the branching
module documentation.
Lists and Iterators
To render an iterator use the for
keyword:
// `ListIteratorExt` is included in the prelude
use kobold::prelude::*;
#[component]
fn IterateNumbers(count: u32) -> impl View {
view! {
<ul>
{
for (1..=count).map(|n| view! { <li> "Item #"{n} })
}
}
}
On updates the iterator is consumed once and all items are diffed with the previous version. No allocations are made by Kobold when updating such a list, unless the rendered list needs to grow past its original capacity.
For more information about keywords visit the keywords
module documentation.
Borrowed Values
View
types are truly transient and only need to live for the duration of the initial render,
or for the duration of the subsequent update. This means that you can easily and cheaply render borrowed
state without unnecessary clones:
#[component]
fn Users<'a>(names: &'a [&'a str]) -> impl View + 'a {
view! {
<ul>
{
for names.iter().map(|name| view! { <li> { name } })
}
}
}
Components with Children
If you wish to capture children from parent view!
invocation, simply change
#[component]
to #[component(children)]
:
use kobold::prelude::*;
#[component(children)]
fn Header(children: impl View) -> impl View {
view! {
<header><h1>{ children }</h1></header>
}
}
fn main() {
kobold::start(view! {
<Header>"Hello Kobold"</Header>
});
}
You can change the name of the parameter used and even set it to a concrete:
use kobold::prelude::*;
// Capture children into the argument `n`
#[component(children: n)]
fn AddTen(n: i32) -> i32 {
// integers implement `View` so they can be passed by value
n + 10
}
fn main() {
kobold::start(view! {
<p>
"Meaning of life is "
<AddTen>{ 32 }</AddTen>
</p>
});
}
More Examples
To run Kobold you'll need to install trunk
(check the full instructions if you have problems):
cargo install --locked trunk
You might also need to add the Wasm target to Rust:
rustup target add wasm32-unknown-unknown
Then just run an example:
## Go to an example
cd examples/todomvc
## Run with trunk
trunk serve
Acknowledgements
- Pedrors for the Kobold logo.
License
Kobold is free software, and is released under the terms of the Mozilla Public License version 2.0. See LICENSE.
Dependencies
~170KB