blob: 7daa28ad2a854a809d5f1492ea85f7f94a2a5a9f [file] [log] [blame]
import {
isArray
} from "../utils";
import {
noop,
resolve,
reject,
subscribe,
PENDING
} from '../-internal';
/**
`Promise.race` returns a new promise which is settled in the same way as the
first passed promise to settle.
Example:
```javascript
var promise1 = new Promise(function(resolve, reject){
setTimeout(function(){
resolve('promise 1');
}, 200);
});
var promise2 = new Promise(function(resolve, reject){
setTimeout(function(){
resolve('promise 2');
}, 100);
});
Promise.race([promise1, promise2]).then(function(result){
// result === 'promise 2' because it was resolved before promise1
// was resolved.
});
```
`Promise.race` is deterministic in that only the state of the first
settled promise matters. For example, even if other promises given to the
`promises` array argument are resolved, but the first settled promise has
become rejected before the other promises became fulfilled, the returned
promise will become rejected:
```javascript
var promise1 = new Promise(function(resolve, reject){
setTimeout(function(){
resolve('promise 1');
}, 200);
});
var promise2 = new Promise(function(resolve, reject){
setTimeout(function(){
reject(new Error('promise 2'));
}, 100);
});
Promise.race([promise1, promise2]).then(function(result){
// Code here never runs
}, function(reason){
// reason.message === 'promise 2' because promise 2 became rejected before
// promise 1 became fulfilled
});
```
An example real-world use case is implementing timeouts:
```javascript
Promise.race([ajax('foo.json'), timeout(5000)])
```
@method race
@static
@param {Array} promises array of promises to observe
@param {String} label optional string for describing the promise returned.
Useful for tooling.
@return {Promise} a promise which settles in the same way as the first passed
promise to settle.
*/
export default function race(entries, label) {
/*jshint validthis:true */
var Constructor = this;
var promise = new Constructor(noop, label);
if (!isArray(entries)) {
reject(promise, new TypeError('You must pass an array to race.'));
return promise;
}
var length = entries.length;
function onFulfillment(value) {
resolve(promise, value);
}
function onRejection(reason) {
reject(promise, reason);
}
for (var i = 0; promise._state === PENDING && i < length; i++) {
subscribe(Constructor.resolve(entries[i]), undefined, onFulfillment, onRejection);
}
return promise;
}