Question

empty

函数签名: empty(scheduler: Scheduler): Observable

立即完成的 observable 。

示例

示例 1: empty 会立即完成

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { empty } from 'rxjs';

// 输出: 'Complete!'
const subscribe = empty().subscribe({
  next: () => console.log('Next'),
  complete: () => console.log('Complete!')
});

示例 2: 使用定时器的 empty

( StackBlitz )

// RxJS v6+
import { interval, fromEvent, merge, empty } from 'rxjs';
import { switchMap, scan, takeWhile, startWith, mapTo } from 'rxjs/operators';

const countdownSeconds = 10;
const setHTML = id => val => (document.getElementById(id).innerHTML = val);
const pauseButton = document.getElementById('pause');
const resumeButton = document.getElementById('resume');
const interval$ = interval(1000).pipe(mapTo(-1));

const pause$ = fromEvent(pauseButton, 'click').pipe(mapTo(false));
const resume$ = fromEvent(resumeButton, 'click').pipe(mapTo(true));

const timer$ = merge(pause$, resume$)
  .pipe(
    startWith(true),
    // 如果定时器暂停，则返回空的 Observable
    switchMap(val => (val ? interval$ : empty())),
    scan((acc, curr) => (curr ? curr + acc : acc), countdownSeconds),
    takeWhile(v => v >= 0)
  )
  .subscribe(setHTML('remaining'));

其他资源

• empty :newspaper: - 官方文档
• Creation operators: empty, never, and throw :video_camera: :dollar: - André Staltz

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源码: https://github.com/ReactiveX/rxjs/blob/master/src/internal/observable/EmptyObservable.ts