Promise.race()

The Promise.race(iterable) method returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects, with the value or reason from that promise.

Syntax

Promise.race(iterable);

Parameters

iterable
An iterable object, such as an Array. See iterable.

Return value

A Promise that resolves or rejects as soon as one of the promises in the given iterable resolves or rejects.

Description

The race function returns a Promise that is settled the same way as the first passed promise to settle. It resolves or rejects, whichever happens first.

Examples

Using Promise.race – examples with setTimeout

var p1 = new Promise(function(resolve, reject) { 
    setTimeout(resolve, 500, "one"); 
});
var p2 = new Promise(function(resolve, reject) { 
    setTimeout(resolve, 100, "two"); 
});

Promise.race([p1, p2]).then(function(value) {
  console.log(value); // "two"
  // Both resolve, but p2 is faster
});

var p3 = new Promise(function(resolve, reject) { 
    setTimeout(resolve, 100, "three");
});
var p4 = new Promise(function(resolve, reject) { 
    setTimeout(reject, 500, "four"); 
});

Promise.race([p3, p4]).then(function(value) {
  console.log(value); // "three"
  // p3 is faster, so it resolves               
}, function(reason) {
  // Not called
});

var p5 = new Promise(function(resolve, reject) { 
    setTimeout(resolve, 500, "five"); 
});
var p6 = new Promise(function(resolve, reject) { 
    setTimeout(reject, 100, "six");
});

Promise.race([p5, p6]).then(function(value) {
  // Not called              
}, function(reason) {
  console.log(reason); // "six"
  // p6 is faster, so it rejects
});

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Promise.race' in that specification.
Standard Initial definition in an ECMA standard.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Promise.race' in that specification.
Draft  

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari Servo
Basic Support32.0(Yes)29.0No support197.1No support
Feature Android Chrome for Android Edge Mobile Firefox for Android IE Mobile Opera Mobile Safari Mobile
Basic Support4.4.432.0(Yes)29No support(Yes)8.0

See also

Document Tags and Contributors

 Contributors to this page: fscholz, eduardoboucas, axelf4, realityking
 Last updated by: fscholz,