Understanding promise.race() usage

Question

As far as I know, there are two options about promise:

• promise.all()

• promise.race()

Ok, I know what promise.all()<

Answer 1

As you see, the race() will return the promise instance which is firstly resolved or rejected:

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
});

For a scenes to be used， maybe you want to limit the cost time of a request ：

var p = Promise.race([
    fetch('/resource-that-may-take-a-while'),
    new Promise(function (resolve, reject) {
         setTimeout(() => reject(new Error('request timeout')), 5000)
    })
])
p.then(response => console.log(response))
p.catch(error => console.log(error))

With the race() you just need to get the returned promise, you needn't care about which one of the promises in the race([]) firstly returned,

However, without the race, just like your example, you need to care about which one will firstly returned, and called the callback in the both success callback.