text: // var async = require("async");
  var sleep = function (time) {
      return new Promise(function (resolve, reject) {
          setTimeout(function () {
              resolve();
          }, time);
      })
  };
  
  var start = async function () {
      // 在这里使用起来就像同步代码那样直观
      console.log('start');
      await sleep(3000);
      console.log('end');
  };
  
  start();
  