race

signature: race(): Observable

The observable to emit first is used.

Ultimate RxJS

Examples

Example 1: race with 4 observables

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { mapTo } from 'rxjs/operators';
import { interval } from 'rxjs/observable/interval';
import { race } from 'rxjs/observable/race';
//take the first observable to emit
const example = race(
//emit every 1.5s
interval(1500),
//emit every 1s
interval(1000).pipe(mapTo('1s won!')),
//emit every 2s
interval(2000),
//emit every 2.5s
interval(2500)
);
//output: "1s won!"..."1s won!"...etc
const subscribe = example.subscribe(val => console.log(val));

Example 2: race with an error

( StackBlitz | jsFiddle )

// RxJS v6+
import { delay, map } from 'rxjs/operators';
import { of, race } from 'rxjs';
//Throws an error and ignores the other observables.
const first = of('first').pipe(
delay(100),
map(_ => {
throw 'error';
})
);
const second = of('second').pipe(delay(200));
const third = of('third').pipe(delay(300));
// nothing logged
race(first, second, third).subscribe(val => console.log(val));

Additional Resources

  • race

    📰 - Official docs

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