// RxJS v6+
import { of } from 'rxjs';
import { takeWhile } from 'rxjs/operators';
​
//emit 1,2,3,4,5
const source$ = of(1, 2, 3, 4, 5);
​
//allow values until value from source is greater than 4, then complete
source$
  .pipe(takeWhile(val => val <= 4))
  // log: 1,2,3,4
  .subscribe(val => console.log(val));

// RxJS v6.4+
import { of } from 'rxjs';
import { takeWhile, filter } from 'rxjs/operators';
​
const source$ = of(1, 2, 3, 9);
​
source$
  // with inclusive flag, the value causing the predicate to return false will also be emitted
  .pipe(takeWhile(val => val <= 3, true))
  // log: 1, 2, 3, 9
  .subscribe(console.log);

// RxJS v6+
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));