Rxjs takeWhile 和 filter 操作符的差別

import { of } from 'rxjs';
import { takeWhile, filter } from 'rxjs/operators';

// emit 3, 3, 3, 9, 1, 4, 5, 8, 96, 3, 66, 3, 3, 3
const source$ = of(3, 3, 3, 9, 1, 4, 5, 8, 96, 3, 66, 3, 3, 3);

// allow values until value from source equals 3, then complete
source$
  .pipe(takeWhile(it => it === 3))
  // log: 3, 3, 3
  .subscribe(val => console.log('takeWhile', val));

source$
  .pipe(filter(it => it === 3))
  // log: 3, 3, 3, 3, 3, 3, 3
  .subscribe(val => console.log('filter', val));
      

差別一目了然：

• takeWhile, 當條件不滿足時，Observable 設定為 completed 狀态，停止 emit 值
• filter, Observable 裡所有滿足條件的值都将被 emit