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Vanilla Reactive System
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| // Credit Ryan Carniato https://frontendmasters.com/courses/reactivity-solidjs/ | |
| let context = []; | |
| export function untrack(fn) { | |
| const prevContext = context; | |
| context = []; | |
| const res = fn(); | |
| context = prevContext; | |
| return res; | |
| } | |
| function cleanup(observer) { | |
| for (const dep of observer.dependencies) { | |
| dep.delete(observer); | |
| } | |
| observer.dependencies.clear(); | |
| } | |
| function subscribe(observer, subscriptions) { | |
| subscriptions.add(observer); | |
| observer.dependencies.add(subscriptions); | |
| } | |
| export function createSignal(value) { | |
| const subscriptions = new Set(); | |
| const read = () => { | |
| const observer = context[context.length - 1] | |
| if (observer) subscribe(observer, subscriptions); | |
| return value; | |
| } | |
| const write = (newValue) => { | |
| value = newValue; | |
| for (const observer of [...subscriptions]) { | |
| observer.execute(); | |
| } | |
| } | |
| return [read, write]; | |
| } | |
| export function createEffect(fn) { | |
| const effect = { | |
| execute() { | |
| cleanup(effect); | |
| context.push(effect); | |
| fn(); | |
| context.pop(); | |
| }, | |
| dependencies: new Set() | |
| } | |
| effect.execute(); | |
| } | |
| export function createMemo(fn) { | |
| const [signal, setSignal] = createSignal(); | |
| createEffect(() => setSignal(fn())); | |
| return signal; | |
| } |
Example using the reactive system:
import { createSignal, createEffect, createMemo, untrack } from "./reactive"; const [count, setCount] = createSignal(0); const [count2, setCount2] = createSignal(2); const [show, setShow] = createSignal(true); const sum = createMemo(() => count() + count2()); createEffect(() => { console.log(count(), count2(), sum()); console.log(untrack(() => count())); }); // 0 setShow(false); setCount(10);
And this is what the code above would print:
0 2 2
0
10 2 12
10
10 2 12
10
impressive!
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Example using the reactive system: