Signal
A Signal is a reactive primitive used to manage state. Signals hold a value that can be read and updated. When the value changes, any subscribers to the signal are notified, allowing for efficient updates to dependent components.
General Usage
Creating a Signal
import { signal } from "kaioken"
const userName = signal("bob")
signal
takes an initial value and optionally a displayName
for debugging. It returns an instance of the Signal
class with the
following properties:
- value: Gets or sets the signal's current value
- subscribe: Registers a function to be called when the signal's value changes
- map: Derives a new signal based on the current signal's value
- peek: Retrieves the value without tracking reactivity
- sneak: Sets the value without emitting a signal change
- notify: Emits a signal change
Reading and Writing Signal Values
You can access a signal's value directly:
console.log(userName.value) // "bob"
userName.value = "alice"
Assigning a new value triggers reactivity, notifying any subscribers.
If you mutate the signal's value without assigning to the value
property,
eg. mySignal.value.something = "test"
, the signal will not notify subscribers.
In this case, use mySignal.notify()
to manually trigger an update.
Subscribing to Signals
You can subscribe to a signal's value changes using the subscribe
method:
const unsubscribe = userName.subscribe((newValue) => {
console.log("Value updated:", newValue)
})
The subscribe function returns an unsubscribe
function,
allowing you to remove the subscription when needed:
unsubscribe()
Computed
Use computed
to create a signal derived from a getter function:
import { computed } from "kaioken"
const userGreeting = computed(() => `Hello, ${userName}!`)
The computed
signal will automatically track dependencies and
update whenever the tracked signals change.
We've snuck a quality-of-life feature in here - signals
implement toString()
and therefore are able to be used in strings.
Watch
Going forward, we'll refer to the act of reading a signal's value as observing. This is one of the more complex, but powerful aspects of signals. The core philosophy around their design is reactivity via observation, where it matters.
Use watch
create a that
will fire the callback whenever observed
signals change.
import { watch } from "kaioken"
const watcher = watch(() => console.log(userGreeting.value))
watcher.stop()
watcher.start()
The callback provided to watch
will fire immediately.
When a signal that it observes
changes, it will be queued to fire again
within a microtask.
This allows us to automatically "batch" execution of callbacks.
In Components
General usage
In Kaioken components, reading and writing signals is slightly nuanced but has the capability to provide unmatched performance.
function App() {
return (
<div>
<h1>{userGreeting.value}</h1>
<input
type="text"
value={userName.value}
oninput={(e) => userName.value = e.target.value}
/>
</div>
)
}
In the above example, our userGreeting
and userName
signals from earlier
are observed
by the component during render, causing the component to
automatically subscribe to them. This means the component and all of its
children will be updated whenever their values change.
While this may be the desired effect, signals can be much more performant when used for text or attributes. See the following:
function App() {
return (
<div>
<h1>{userGreeting}</h1>
<input
type="text"
value={userName}
oninput={(e) => userName.value = e.target.value}
/>
</div>
)
}
Because neither of the signals are observed
at the time of rendering,
when they change, Kaioken will only change the things that matter - in
this case, the text node inside of our heading that displays the
greeting and the value
attribute of our input.
Using local signals
signal
, computed
, and watch
can all be created locally in Kaioken
components via the useSignal
, useComputed
, and useWatch
hooks.
This will allow them to be persisted across renders and automatically
disposed of when the component unmounts.
import { useSignal, useComputed, useWatch } from "kaioken"
function App() {
const userName = useSignal("bob")
const userGreeting = useComputed(() => `Hello, ${userName}!`)
useWatch(() => console.log(userName.value))
return (
<div>
<h1>{userGreeting}</h1>
<input
type="text"
value={userName}
oninput={(e) => userName.value = e.target.value}
/>
</div>
)
}