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@@ -0,0 +1,69 @@
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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: #aaa;
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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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+ }
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+ p{
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+ font-size: 50px;
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+ color: #fff;
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+ font-weight: bold;
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+ text-align: center;
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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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+ background-color:#fff;
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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 num = document.getElementsByTagName("p")[0];
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+ var btn = document.getElementsByTagName("button")[0];
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+ var timer = 0;
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+ // 第二步：给按钮绑定事件
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+ btn.onclick = function(){
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+ if(btn.innerText == "开始"){
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+ btn.innerText = "暂停";
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+ // 开始倒计时-1
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+ timer = setInterval(function(){
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+ num.innerText--;
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+ },1000)
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+ console.log(timer);
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+ }else{
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+ btn.innerText = "开始"
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+ // 停止定时器
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+ console.log(timer)
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+ clearInterval(timer)
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+ }
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+ }
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+
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+
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+ // 如果使用on绑定事件绑定多次那么后边绑定的会覆盖前面绑定的事件
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+ // var a = 1;
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+ // var a = 2;
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+ // btn.onclick = function(){
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+ // console.log("hello")
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+ // }
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+ </script>
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+</body>
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+</html>
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