常用的JS判断()

<input type="submit" name="Submit2" value="提交" onclick="return tijiao()" />

<script language="javascript">

function tijiao(){
var user
var pass
user=document.getElementById("username").value
pass=document.getElementById("password").value

if (user=="" || pass==""){
 alert("用户名和密码都不能为空")
 return false
}else {
alert("成功") }
}
</script>