倒计时抢购

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport"
content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>倒计时抢购</title>
</head>
<body>
<div id="box"></div>
<script>
~function(){
let box = document.getElementById('box'),
serverTime = null,
autoTimer = null;
//=> 为了时间显示统一,小于10,则补0
let formatTime = (value) => {
value < 10 ? value = `0${value}` : null;
return value
};
let fn = () => {
serverTime += 1000;
let startTime = new Date('2019/6/4 15:31:08').getTime(),
remainTime = startTime - serverTime;
if (remainTime < 0) {
box.innerHTML = '开抢啦!';
clearInterval(autoTimer);
} else {
let hours = Math.floor(remainTime / (1000 * 60 * 60));
remainTime -= hours * 1000 * 60 * 60;
let minute = Math.floor(remainTime / (1000 * 60));
remainTime -= minute * 1000 * 60;
let second = Math.floor(remainTime / 1000);
hours = formatTime(hours);
minute = formatTime(minute);
second = formatTime(second);
box.innerHTML = `距离抢购还有:${hours}:${minute}:${second}`;
}
};

let getServeTime = () => {
let xhr = new XMLHttpRequest();
xhr.onreadystatechange = () => {
//=> 状态码以2|3开头的都代表成功,取反请求失败不做任何操作
if (!/^(2|3)\d{2}$/.test(xhr.status)) return;
//=> 这里要注意因为是请求方式是head,所以 readyState的状态不会出现3
if (xhr.readyState === 2) {
//=> 首次进入页面,请求服务器时间成功后。手动调用fn判断是否到期,然后开启定时函数,每秒在请求回来的服务器时间上+1000ms
serverTime = new Date(xhr.getResponseHeader('date')).getTime();
fn();
autoTimer = setInterval(fn, 1000);
}
};
xhr.open('head', 'data.json', true);
xhr.send();
};
getServeTime();
}();

//=> 重点 1、就是在抢购的活动中,时间要以服务器时间为准
//=> 重点 2、在客户端请求服务端时间的这个过程中,避免不了会存在延迟。这里采用head请求方式,以减少延迟的时间
</script>
</body>
</html>