Signal

A simple, small (< 1kb minified + gzip) library for creating and using signals.

Installation

npm install @axel669/signal

import * as signals from "https://esm.sh/@axel669/[email protected]"

Todo

• maybe don't trigger updates if strict equality is true
• is async signal processing useful?

Usage

Value Signal

The simplest form of signal. It holds a value that can be read or changed and does not depend on other signals directly.

const counter = signal(0)

console.log(counter.value) // logs 0
counter.value += 1
console.log(counter.value) // logs 1

Derived Signal

A signal that takes a function as its argument and calculates a value based on the value of other signals. The function reruns every time one of the signals it relies on changes value. Async functions do not work as the signal recalculation is done synchronously for all signals after updates happen.

const counter = signal(0)
const mod3 = derive(() => counter.value % 3)

console.log(counter.value, mod3.value) // logs 0 0
counter.value = 5
console.log(counter.value, mod3.value) // logs 5 2

Effect Signal

A signal that takes a function and runs some code based on the value of the signals it relies on. Does not have a value output of its own, so it can never be a dependency of another signal, which means it can also handle async functions, since there is no output to wait for within the signal recalculations.

const counter = signal(0)
const logger = effect(() => console.log(counter.value)) // logs 0 at creation

counter.value += 1 // makes the effect signal log 1

Batching

Sometimes it is useful to change more then one value signal before letting their subscribers update, this cam be done by wrapping the changes in a function that is passed to batch.

const a = signal(0)
const b = signal(1)
const logger = effect(() => console.log(a.value, b.value)) // logs 0 1

a.value = 2 // makes the effect signal log 2 1
b.value = 5 // makes the effect signal log 2 5
// only triggers one log of 3 6
batch(
    () => {
        a.value = 3
        b.value = 6
    }
)

Disposing

All signals have a .cleanup function that will disable the effect from sending or receiving updates, and will remove it from all dependency trees. Any signal that has been disposed can still have its value read (if it had one), but the value can no longer be updated, and reading the value will no longer add it to dependency trees.

const a = signal(0)
const b = signal(1)
const sum = derive(() => a.value + b.value)

console.log(a.value, b.value, sum.value) // logs 0 1 1
a.value = 2
console.log(a.value, b.value, sum.value) // logs 2 1 3
a.cleanup()
b.value = 5
console.log(a.value, b.value, sum.value) // logs 2 5 7 because b still updates

Signal IDs

All signals have a .id that can be assigned to, all default to null. This is just a helpful debug tool, it has no functional purpose for the way signals communicate with each other.