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| export function observable<T>(value: T): Observable<T> { | |
| const subscribers = new Set<(val: T) => void>(); | |
| function run(): T; | |
| function run(newValue: T): void; | |
| function run(updateFunction: (oldValue: T) => T): void; | |
| function run(newValueOrUpdateFn?: T | ((oldValue: T) => T)): T | void { | |
| if (newValueOrUpdateFn === undefined) { | |
| return value; | |
| } | |
| const oldValue = value; | |
| if (typeof newValueOrUpdateFn === "function") { | |
| value = (newValueOrUpdateFn as any)(value); | |
| } else { | |
| value = newValueOrUpdateFn; | |
| } | |
| if (oldValue !== value) { | |
| subscribers.forEach((fn) => fn(value)); | |
| } | |
| } | |
| run.subscribe = (fn: (val: T) => void) => { | |
| subscribers.add(fn); | |
| return () => { | |
| subscribers.delete(fn); | |
| }; | |
| }; | |
| return run; | |
| } | |
| export interface Observable<T> { | |
| (): T; | |
| (newValue: T): void; | |
| (val: (oldValue: T) => T): void; | |
| subscribe(fn: (value: T) => void): () => void; | |
| } | |
| const count = observable(0); | |
| const unsubscribe = count.subscribe(console.log); | |
| count(1); // Prints 1 | |
| count((x) => x + 1); // Prints 2 | |
| console.log(count()); // Prints 2 | |
| count(2); // Doesn't print (value unchanged) | |
| unsubscribe(); | |
| count(3); // Doesn't print (unsubscribed) |
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