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@@ -0,0 +1,78 @@
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+<!DOCTYPE html>
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+<html lang="en">
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+<head>
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+ <meta charset="UTF-8">
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+ <meta name="viewport" content="width=device-width, initial-scale=1.0">
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+ <title>Document</title>
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+ <style>
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+ .box{
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+ width: 300px;
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+ height: 300px;
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+ background-color: #999;
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+ border-radius: 20px;
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+ box-shadow: 1px 1px 5px rgba(0,0,0,0.5);
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+ position: fixed;
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+ top: 50%;
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+ left: 50%;
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+ margin-top: -150px;
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+ margin-left: -150px;
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+ text-align: center;
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+ color: #fff;
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+ font-weight: bold;
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+ font-size: 50px;
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+ }
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+ p{
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+ margin-bottom: 0;
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+ margin-top: 80px;
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+ }
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+ button{
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+ width: 100px;
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+ height: 50px;
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+ font-size: 30px;
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+ }
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+ </style>
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+</head>
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+<body>
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+ <div class="box">
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+ <p>100</p>
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+ <button>开始</button>
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+ </div>
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+ <script>
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+ // 第一步 获取要控制的元素
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+ var oNum = document.getElementsByTagName("p");
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+ var oBtn = document.getElementsByTagName("button");
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+ // 定义start变量来控制开始和暂停
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+ var start = true;
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+ // 定义定时器数字
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+ var num = 100;
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+ // 定义定时器变量
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+ var timer = null;
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+
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+ // 定义倒计时函数
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+ function fn(){
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+ timer = setInterval(function(){
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+ num--;
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+ oNum[0].innerText = num;
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+ },1000);
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+ }
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+
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+
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+ // 绑定事件
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+ oBtn[0].onclick = function(){
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+ // 修改按钮中的文字
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+ if(start){
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+ oBtn[0].innerText = "暂停";
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+ start = false;
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+ // 调用倒计时函数
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+ fn();
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+ }else{
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+ oBtn[0].innerText = "开始";
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+ start = true;
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+ // 暂停倒计时
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+ clearInterval(timer);
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+ }
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+
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+ }
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+ </script>
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+</body>
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+</html>
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