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"

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.

Watch

Use watch create a WatchEffect 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>
  )
}