race

signature: race(): Observable

The observable to emit first is used.

Examples

Example 1: race with 4 observables

( StackBlitz | jsBin | jsFiddle )

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 )

import { delay, map } from 'rxjs/operators';
import { of } from 'rxjs/observable/of';
import { race } from 'rxjs/observable/race';

//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));

race(first, second, third).subscribe(val => console.log(val));

Additional Resources

  • race :newspaper: - Official docs

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

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