async

function doubleAfter2seconds(num) {
          return new Promise((resolve, reject) => {
            setTimeout(() => {
              resolve(2 * num)
            }, 2000);
          } )
        }
        async function timeout() {
          let result = await doubleAfter2seconds(30);
          console.log(result);
          return "是"
        }
timeout().then(result => {
          console.log(result);
        })






.......................................................
var data = [
    'https://xxx.com/img/logo.jpg',
    'https://xxx.com/img/bg.jpg',
    'https://xxx.com/css/main.css',
    'https://xxx.com/css/animate.css',
    'https://xxx.com/js/jquery.js',
    'https://xxx.com/js/form.js',
]
data.forEach(request)
function request(url) {
 alert(url)
}