<!DOCTYPE?html>
<html?lang="en">
<head>
????<meta?charset="UTF-8">
????<title>編程練習8</title>??
</head>
<body>?
????<p>
????????<b?id="seconds">5</b>秒后進入新界面
????????<a?href="javascript:goBack();">返回</a>
????</p>
????<form>
????????<input?type="button"?value="取消倒計時"?onclick="quxiao()">
????</form>
????<script?type?=?"text/javascript">
????????function?jisi(){
????????var?sec?=?document.getElementById("seconds");
????????var?i?=?5;
????????var?timer?=?setInterval(function(){
????????i--;
????????sec.innerHTML?=?i;
????????if(i==1){
????????????window.location.href?=??"http://www.xianlaiwan.cn/";
????????}
????},1000);
????????}
????????jisi();
????????function?quxiao(){
????????????clearInterval(timer);
????????}
????</script>
<!--發現如果建立函數jisi則不能建立函數quxiao了，
建立函數就只能使用onclick="clearInterval(timer)"
使用quxiao函數的話就必須不能給上面的代碼建立成一個jisi函數
-->
</body>
</html>
2017-06-03
你把timer的定義寫在jishi函數外面,因為這是一個函數作用域，別的函數獲取不到這個變量的
var?timer; ????????function?jisi(){ ????????var?sec?=?document.getElementById("seconds"); ????????var?i?=?5; ?????????timer?=?setInterval(function(){ ????????i--; ????????sec.innerHTML?=?i; ????????if(i==1){ ????????????window.location.href?=??"http://www.xianlaiwan.cn/"; ????????} ????},1000); ????????} ????????jisi(); ????????function?quxiao(){ ????????????clearInterval(timer); ????????}