Created
February 1, 2021 09:11
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| interface Person { | |
| name: string; | |
| surname: string; | |
| } | |
| type StringKeys<T> = string & keyof T; | |
| type KeyChangedCallback<T> = (key: StringKeys<T>, obj: T) => void; | |
| type UnsubscribeFn = () => void; | |
| type KeyChangeObservable<T> = T & { onKeyChanged: (keyName: StringKeys<T>, cb: KeyChangedCallback<T>) => UnsubscribeFn } | |
| function newKeyChangeWatcher<T extends object>(obj: T): KeyChangeObservable<T> { | |
| const callbacks: { [k in StringKeys<T>]?: KeyChangedCallback<T>[] } = {} | |
| const subscribe = (keyName: StringKeys<T>, cb: KeyChangedCallback<T>): UnsubscribeFn => { | |
| callbacks[keyName] ||= []; | |
| callbacks[keyName]!.push(cb); | |
| const unsubscribe = () => { | |
| callbacks[keyName] = callbacks[keyName]!.filter(storedCb => storedCb !== cb); | |
| }; | |
| return unsubscribe | |
| } | |
| const proxy = new Proxy(obj, { | |
| set(target, prop, value, _receiver): boolean { | |
| const key = prop as StringKeys<T>; | |
| target[key] = value; | |
| if (prop in callbacks) { | |
| callbacks[key]!.forEach((cb) => { | |
| cb(key, target); | |
| }) | |
| } | |
| return true; | |
| }, | |
| }) as KeyChangeObservable<T>; | |
| proxy.onKeyChanged = (keyName, cb) => { | |
| return subscribe(keyName, cb); | |
| } | |
| return proxy; | |
| } | |
| let p: Person = { | |
| name: 'Person', | |
| surname: 'Personov', | |
| } | |
| const newOnKeyChangedCallback = (subscriberId: number): KeyChangedCallback<Person> => { | |
| return (key, person) => { | |
| console.log(`Subscriber ${subscriberId}: ${key} -> ${person[key]}`); | |
| }; | |
| } | |
| let observableP = newKeyChangeWatcher(p); | |
| const unsubscribe1 = observableP.onKeyChanged("name", newOnKeyChangedCallback(1)) | |
| const unsubscribe2 = observableP.onKeyChanged("name", newOnKeyChangedCallback(2)) | |
| const unsubscribe3 = observableP.onKeyChanged("surname", newOnKeyChangedCallback(3)) | |
| for (let i = 0; i < 10; i++) { | |
| observableP.name = `Person ${i}`; | |
| if (i === 3) unsubscribe1(); | |
| if (i === 7) unsubscribe2(); | |
| } | |
| for (let i = 0; i < 5; i++) { | |
| observableP.surname = `Personov ${i}`; | |
| if (i === 3) unsubscribe3(); | |
| } | |
| console.log(observableP); |
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