這是我的60秒計時代碼,它運行成功。爲什麼不能設置`document.getElementById(「text」); 「成爲全球?
<html>
<head>
<script type="text/javascript">
var start=Date.now();
function showtime(){
var c=document.getElementById("text");
var nowtime=60-Math.floor((Date.now()-start)/1000);
c.innerHTML="left time is "+ nowtime +" seconds";
}
function countTime(){
var c=document.getElementById("text");
c.innerHTML="left time is 60 seconds";
setInterval("showtime()",1000);
}
</script>
</head>
<body onload="countTime()">
<div id="text"></div>
</body>
</html>
這裏var start=Date.now()
使啓動一個全局變量,爲什麼var c=document.getElementById("text");
不能行var start=Date.now();
寫在下面,使變量c作爲全局變量?
<html>
<head>
<script type="text/javascript">
var start=Date.now();
var c=document.getElementById("text");
function showtime(){
var nowtime=60-Math.floor((Date.now()-start)/1000);
c.innerHTML="left time is "+ nowtime +" seconds";
}
function countTime(){
c.innerHTML="left time is 60 seconds";
setInterval("showtime()",1000);
}
</script>
</head>
<body onload="countTime()">
<div id="text"></div>
</body>
</html>
請解釋爲什麼該程序無法運行時設置document.getElementById("text");
的詳細全球。