zip

signature: zip(observables: *): Observable

After all observables emit, emit values as an array

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💡 Combined with interval or timer, zip can be used to time output from another source!

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Examples

Example 1: zip multiple observables emitting at alternate intervals

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { delay } from 'rxjs/operators';
import { of, zip } from 'rxjs';

const sourceOne = of('Hello');
const sourceTwo = of('World!');
const sourceThree = of('Goodbye');
const sourceFour = of('World!');
//wait until all observables have emitted a value then emit all as an array
const example = zip(
  sourceOne,
  sourceTwo.pipe(delay(1000)),
  sourceThree.pipe(delay(2000)),
  sourceFour.pipe(delay(3000))
);
//output: ["Hello", "World!", "Goodbye", "World!"]
const subscribe = example.subscribe(val => console.log(val));

Example 2: zip when 1 observable completes

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { take } from 'rxjs/operators';
import { interval, zip } from 'rxjs';

//emit every 1s
const source = interval(1000);
//when one observable completes no more values will be emitted
const example = zip(source, source.pipe(take(2)));
//output: [0,0]...[1,1]
const subscribe = example.subscribe(val => console.log(val));

Example 3: get X/Y coordinates of drag start/finish (mouse down/up)

( StackBlitz )

// RxJS v6+
import { fromEvent, zip } from 'rxjs';
import { map } from 'rxjs/operators';

const documentEvent = eventName =>
  fromEvent(document, eventName).pipe(
    map((e: MouseEvent) => ({ x: e.clientX, y: e.clientY }))
  );

zip(documentEvent('mousedown'), documentEvent('mouseup')).subscribe(e =>
  console.log(JSON.stringify(e))
);

Example 4: mouse click duration

( StackBlitz )

// RxJS v6+
import { fromEvent, zip } from 'rxjs';
import { map } from 'rxjs/operators';

const eventTime = eventName =>
  fromEvent(document, eventName).pipe(map(() => new Date()));

const mouseClickDuration = zip(
  eventTime('mousedown'),
  eventTime('mouseup')
).pipe(map(([start, end]) => Math.abs(start.getTime() - end.getTime())));

mouseClickDuration.subscribe(console.log);

Additional Resources

• zip 📰 - Official docs

• zip - In Depth Dev Reference

• Combination operator: zip 🎥 💵 - André Staltz

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📁 Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/zip.ts