<!DOCTYPE?html>
<html?lang="en">
<head>
????<meta?charset="UTF-8">
????<title>Title</title>
????<script>
????????function?start()?{
????????????var?today?=?new?Date();
????????????document.getElementById("txt").innerHTML=today.getHours()+":"+today.getMinutes()+":"+today.getSeconds();
????????????i=setInterval("start()",1000)
????????}
????????function?stop()?{
????????????clearInterval(i);
????????}
????</script>
</head>
<body>
<button?onclick="start()">單擊這里</button>
<button?onclick="stop()">單擊這里</button>
<div?id="txt"?></div>
</body>
</html>
2019-07-25
第一個(gè)問(wèn)題：你的i變量是start內(nèi)部的，stop函數(shù)訪問(wèn)不到start的作用域
點(diǎn)擊第一個(gè)按鈕時(shí)候觸發(fā)start函數(shù)，該函數(shù)內(nèi)部會(huì)觸發(fā)定時(shí)器。定時(shí)器會(huì)重新觸發(fā)函數(shù)，你的定時(shí)器會(huì)有多個(gè)，有定時(shí)器存在的時(shí)候一定不要重復(fù)啟動(dòng)定時(shí)器。要全局維持一個(gè)定時(shí)器。
下邊正確代碼，忘采納