es6/7 async

function ajaxA() {
    return new Promise(function(resolve, reject) {
      setTimeout(function() {
        resolve('5s后返回的数值');
      }, 5000)
    })
  }

  function ajaxB() {
    return new Promise(function(resolve, reject) {
      setTimeout(function() {
        resolve('10s后返回的数值');
      }, 10000)
    })
  }

  async function a() {
    // var x = await ajaxA();
    // var y = await ajaxB();
    // 15s后输出x,y
    let [x, y] = await Promise.all([ajaxA(), ajaxB()]);
    console.log(x, y);
  }
  a();
// 10s后输出x,y