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import {
isArray
} from "../utils";
/**
`Promise.race` returns a new promise which is settled in the same way as the
first passed promise to settle.
Example:
```javascript
let promise1 = new Promise(function(resolve, reject){
setTimeout(function(){
resolve('promise 1');
}, 200);
});
let 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
let promise1 = new Promise(function(resolve, reject){
setTimeout(function(){
resolve('promise 1');
}, 200);
});
let 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
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) {
/*jshint validthis:true */
let Constructor = this;
if (!isArray(entries)) {
return new Constructor((_, reject) => reject(new TypeError('You must pass an array to race.')));
} else {
return new Constructor((resolve, reject) => {
let length = entries.length;
for (let i = 0; i < length; i++) {
Constructor.resolve(entries[i]).then(resolve, reject);
}
});
}
}
|
