switchMap相关文章

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Projects each source value to an Observable which is merged in the output Observable, emitting values only from the most recently projected Observable.

理解记忆法：switchMap -> switch to a new Observable，亦即SwitchMap返回的OperatorFunction，其function的输出是一个新的Observable.

例子：

const switched = of(1, 2, 3).pipe(switchMap((x: number) => of(x, x ** 2, x ** 3)));switched.subscribe(x => console.log(x));

输出：

/*const switched = of(1, 2, 3).pipe(switchMap((x: number) => of(x, x ** 2, x ** 3)));switched.subscribe(x => console.log(x));*/const origin = of(1, 2, 3);// fn是一个函数，接受一个number输入，返回一个Observable对象，包含3个number元素const fn = (x: number) => of(x, x ** 2, x ** 3);// OperatorFunction:尖括号里前一个number是输入类型// 第二个括号是输出类型const mapper: OperatorFunction<number, number> = switchMap(fn);// pipe需要接受的类型是OperatorFunction，经过operator传入一个// funcion进去组合而成const switched = origin.pipe(mapper);switched.subscribe(x => console.log('diablo: ' + x));

总结：OperatorFunction的类型很形象，由Operator接收一个function作为输入，组装而成

switchMapTo

const origin = of(111, 222, 333);const copy = origin.pipe(map( (x) => x + 1));// observable: ObservableInput<R>const int = interval(1000).pipe(take(3));const fn = (x: number) => of(x, x ** 2, x ** 3);// 需要传一个Observable进去const mapper = switchMapTo(int);const switched = origin.pipe(mapper);switched.subscribe(x => console.log('diablo2: ' + x));

测试结果：origin里的value完全没有被考虑：

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