為什么不能直接調(diào)用startCount();
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>計(jì)時(shí)器</title>
</head>
<script type="text/javascript">
? var num=0;
? function startCount() {
??? document.getElementById('count').value=num;
??? num=num+1;
??? setTimeout("startCount()",1000);
? }
? startCount();
? //setTimeout("startCount()",0);
</script>
</head>
<body>
<form>
<input type="text" id="count" />
</form>
</body>
</html>
2015-10-09
<!DOCTYPE?HTML> <html> <head> <meta?http-equiv="Content-Type"?content="text/html;?charset=utf-8"> <title>計(jì)時(shí)器</title> </head> </head> <body> <form> ????<input?type="text"?id="count"?value=""?/> </form> <script?type="text/javascript"> ??var?num=0; ??function?startCount()?{ ????document.getElementById('count').value?=?num; ????num=num+1; ????setTimeout("startCount()",1000);? ??} ??startCount(); </script> </body> </html>原因是你程序一開始就被執(zhí)行。系統(tǒng)還沒(méi)有獲取到input這個(gè)標(biāo)簽。導(dǎo)致document.getElementById('count').value這報(bào)錯(cuò)。
2015-10-09
把startCount();改成setTimeout(startCount,1000);就能執(zhí)行了···具體我也不知道為什么···?