<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>登录</title>
</head>
<script language="JavaScript">
var a = document.getElementById("user").value;
var b = document.getElementById("pas").value;
function check(){
if(a.length==0){
alert("请输入账号")
}else{
if(b.length==0){
alert("请输入密码")
}
}
}
</script>
<body>
<form >
<div id="">
<table >
<tr>
<td>账号</td>
<td><input name="user" type="text" id="user"></td>
</tr>
<tr>
<td>密码</td>
<td><input name="pas" type="text" id="pas"></td>
</tr>
<tr>
<td>
<button onclick="check()">登录</button>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
两个值都不能获取
获取属性值没错；
你得写到 函数里面喔；
a b获取值要写在函数里面
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>登录</title>
</head>
<body>
<form>
<div id="">
<table>
<tr>
<td>账号</td>
<td><input name="user" type="text" id="user" /></td>
</tr>
<tr>
<td>密码</td>
<td><input name="pas" type="text" id="pas" /></td>
</tr>
<tr>
<td>
<button onclick="check1()">登录</button>
</td>
</tr>
</table>
</div>
</form>
</body>
<script type="text/javascript">
function check1(){
var a = document.getElementById("user").value;
var b = document.getElementById("pas").value;
if(a.length==0){
alert("请输入账号");
}else{
if(b.length==0){
alert("请输入密码");
}
}
}
</script>
</html>