1. Promise.all()和Promise.race() 并行调用异步操作

两个函数均用于并行调用多个异步操作使用

• All：两个异步操作都resolve之后调用then()

var p1 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 500, 'P1');
});
var p2 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 600, 'P2');
});
// 同时执行p1和p2，并在它们都完成后执行then:
Promise.all([p1, p2]).then(function (results) {
    console.log(results); // 获得一个Array: ['P1', 'P2']
});

• Race：最快的异步操作resolve后调用then()

var p1 = new Promise(function (resolve, reject) {
   setTimeout(resolve, 500, 'P1');
});
var p2 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 600, 'P2');
});
// 同时执行p1和p2，最快返回函数执行then:
Promise.race([p1, p2]).then(function (results) {
    console.log(results); // 'P1'
});