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You often need to render out data before you stream begins from a click or another user interaction. This lessons shows how to use startWith to set the initial output before you trigger your stream.
const Observable = Rx.Observable; const startButton = document.querySelector(‘#start‘); const stopButton = document.querySelector(‘#stop‘); const start$ = Observable.fromEvent(startButton, ‘click‘); const interval$ = Observable.interval(1000); const stop$ = Observable.fromEvent(stopButton, ‘click‘); const intervalThatStops$ = interval$ .takeUntil(stop$); const data = {count: 0}; start$ .switchMapTo(intervalThatStops$) .startWith(data) .scan( (acc) => { return Object.assign(acc, {count: acc.count + 1}) }) .subscribe((x)=> console.log(x));
What startWith will do is, before you click the start button, it will set the initial value for scan(), and logout 0 on the screen.
Then when you click the start button, it will increase from 1 to .....
So it means startWith actually will fire subscrie once.
[RxJS] Displaying Initial Data with StartWith
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原文地址：http://www.cnblogs.com/Answer1215/p/5258848.html
