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

Browser compatibility

See also

• Promise
• Promise.all()