通过rxjs的一个例子, 来学习SwitchMap的使用方法

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源代码：

import { Observable, of, OperatorFunction } from "rxjs";

import { map } from "rxjs/operators";

import { interval } from "rxjs";

import { switchMap } from "rxjs/operators";

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

switchMap将source value映射成一个新的Observable，这个Observable被output Observable自动merge.

只会从最新的被projected过后的Observable里emit数据

给consumer

*/

const add100 = (counter: number) => {

 return of(counter + 100);

};

const addFunctionOperator: OperatorFunction = switchMap(add100);

const pollTasks = () => {

 return interval(1000).pipe(addFunctionOperator);

// caller can do subscription and store it as a handle:

let tasksSubscription = pollTasks().subscribe(data =>

 console.log("timestamp: " + new Date() + ": " + data)

);

// turn it off at a later time

setTimeout(() => tasksSubscription.unsubscribe(), 3000);