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

See also

• Promise
• Promise.all()