這應該是屬於入門級的js文章了，我們js 判斷變數是否為空實例簡單介紹一下吧。
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "HTTP://www.w3.org/tr/xhtml1/dtd/ xhtml1-transitional.dtd">
<html xmlns="HTTP://www.w3.org/1999/xhtml">
<head>
<meta HTTP-equiv="content-type" content="text/html; charset=gb2312" />
<title>js 判斷變數是否為空</title>
<script>
function s(){
var tt=document.getelementbyid("dw").value;
alert(tt);
if(tt==null || tt==""){
alert("輸入內容，不能為空哦");
}
else{
alert(tt);
}
return false;
}
</script>
</head>
<body>
<form id="form1" name="form1" method="post" action="">
<label for="textfield"></label>
<input type="text" name="dw" id="dw" />
<input type="submit" name="button" id="button" value="提交" onclick="網頁特效:return s();" />
</form>
</body>
</html>
那肯定變數不是空的啊，教你一種方法，你這樣寫：
function s(){
var tt=document.getelementbyid("dw").value;
ssssss();//程式運行至此會報錯，點擊調試，用調試工具跟進來看看到底什麼情況
if(tt!=null){
alert("bukong");
}
else{
alert("kong");
}
}
另，附一個判斷是否為空的方法：
var isnull = function(obj)
{
try{return obj==0?false:!obj}catch(e){return false;}
}
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