要求：请求5次ajax,将结果依次显示在页面

老办法：用数组+定时器代替for循环

 function getTime(j, length) {
            setTimeout(function () {
                $start = new Date().getTime();
                $.get(seturl, function (e) {
                    $end = new Date().getTime();
                    //js请求时间
                    //计算出相差天数
                    $date = $end - $start;
                    $seconds = Math.ceil($date / (1000));
                    $last = $seconds - e['time'];
                    console.log($seconds);
                    $html = $('<li>' + j + '  test1: ' + e["time"] + 's' + '   /   test2:  ' + $last + 's</li>');
                    $html.appendTo($('.list'));
                    //成功后，判断是否要接着执行
                    if (++j < length) {
                        getTime(j, length);
                    }
                    if (j == 6) {
                        //loading end
                        $('#loading').hide();
                    }
                }, 'json').error(function (XMLHttpRequest, textStatus, errorThrown) {
                    alert(XMLHttpRequest.status);
                    alert(XMLHttpRequest.readyState);
                    alert(textStatus);
                })
            }, Math.random() * 3000);
        }
        getTime(1, 6);

新办法：ES6 async await

```
async function getTime() {
for (var i = 1; i <6 ; i++) {
await Time(i);
}
}

  function Time(j) {
        $start = new Date().getTime();
        $.get(seturl, function (e) {
            $end = new Date().getTime();
            //js请求时间
            //计算出相差天数
            $date = $end - $start;
            $seconds = Math.ceil($date / (1000));
            $last = $seconds - e['time'];
            //显示在页面上
            $html = $('<li>' + j + '  test1: ' + e["time"] + 's' + '   /   test2:  ' + $last + 's</li>');
            $html.appendTo($('.list'));
            if (j == 5) {
            // loading end
            $('#loading').hide();
            }
        }, 'json').error(function (XMLHttpRequest, textStatus, errorThrown) {
            alert(XMLHttpRequest.status);
            alert(XMLHttpRequest.readyState);
            alert(textStatus);
        })
    }

getTime();

```