Promise.race

【Promise.race】

　　返回最先完成的promise

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
});

　　https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/race