为什么用户名为空的时候div内容没有变更呢?
<!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=utf-8" />
<title>云南大学自习室系统</title>
<script type="text/javascript">
<!--
function validity(){
var userinfo=document.getElementById("uerr");
var passinfo=document.getElementById("perr");
if(loginform.username.value == "") {
userinfo.innerHTML = "用户名错误" ;
}
if (loginform.password.value == "") {
passinfo.innerHTML = "密码错误";
}
}
-->
</script>
</head>
<body>
<form id="loginform" name="loginform" method="post" action="">
<table width="354" height="176" border="0">
<tr>
<td colspan="2">云南大学自习室系统</td>
</tr>
<tr>
<td width="">用户名</td>
<td>
<input type="text" name="username" id="username"/> </td>
</tr>
<tr><td colspan="2"><div id="uerr"></div></td></tr>
<tr>
<td>密码</td>
<td>
<input type="password" name="password" id="password"/> </td>
</tr>
<tr><td colspan="2"><div id="perr"></div></td></tr>
<tr>
<td><input type="submit" name="Submit" value="登录" onClick="validity();"></td>
<td> </td>
</tr>
</table>
</form>
</body>
</html>
<!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=utf-8" />
<title>云南大学自习室系统</title>
<script type="text/javascript">
<!--
function validity(){
var userinfo=document.getElementById("uerr");
var passinfo=document.getElementById("perr");
if(loginform.username.value == "") {
userinfo.innerHTML = "用户名错误" ;
}
if (loginform.password.value == "") {
passinfo.innerHTML = "密码错误";
}
}
-->
</script>
</head>
<body>
<form id="loginform" name="loginform" method="post" action="">
<table width="354" height="176" border="0">
<tr>
<td colspan="2">云南大学自习室系统</td>
</tr>
<tr>
<td width="">用户名</td>
<td>
<input type="text" name="username" id="username"/> </td>
</tr>
<tr><td colspan="2"><div id="uerr"></div></td></tr>
<tr>
<td>密码</td>
<td>
<input type="password" name="password" id="password"/> </td>
</tr>
<tr><td colspan="2"><div id="perr"></div></td></tr>
<tr>
<td><input type="submit" name="Submit" value="登录" onClick="validity();"></td>
<td> </td>
</tr>
</table>
</form>
</body>
</html>
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if(document.getElementById('username').value == '')
...
其次登陆按钮类型是submit,也就是说点击登陆按钮一定会刷新画面。就算是检查出错误也会被刷新。所以将submit改为button<!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=utf-8" />
<title>云南大学自习室系统</title>
<script type="text/javascript">
<!--
function validity(){
var userinfo=document.getElementById("uerr");
var passinfo=document.getElementById("perr");
var loginform = document.getElementById("loginform");
var check = true;
if(loginform.username.value == "") {
userinfo.innerHTML = "用户名错误" ;
check = false;
}
if (loginform.password.value == "") {
passinfo.innerHTML = "密码错误";
check = false;
}
if (check) loginform.submit();
}
-->
</script>
</head> <body>
<form id="loginform" name="loginform" method="post" action="">
<table width="354" height="176" border="0">
<tr>
<td colspan="2">云南大学自习室系统</td>
</tr><tr>
<td width="">用户名
</td><td>
<input type="text" name="username" id="username"/>
</td>
</tr><tr>
<td colspan="2"><div id="uerr"></div></td>
</tr><tr>
<td>密码</td>
<td><input type="password" name="password" id="password"/></td>
</tr><tr>
<td colspan="2"><div id="perr"></div></td>
</tr><tr>
<td><input type="button" name="Submit" value="登录" onClick="validity();"></td>
<td> </td>
</tr>
</table>
</form>
</body>
</html>
其次登陆按钮类型是submit,也就是说点击登陆按钮一定会刷新画面。就算是检查出错误也会被刷新。所以将submit改为button首先你这样理解的只是对了一半,并不是submit就一定会刷新界面,他其实内部 只是默认调了$("form").submit()
<input type="button" name="Submit" value="登录" onClick="return validity();">
把你调用涵数的改成前面加上return ,那么 你涵数里面只要返回false 就可以阻止表单提交了,就算是type="submit" 一样不会提交
2、判断{} 中增加 return false;
3、loginform 没必要定义;
代码在下面:<!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=utf-8" />
<title>云南大学自习室系统</title>
<script type="text/javascript">
<!--
function validity(){
var userinfo=document.getElementById("uerr");
var passinfo=document.getElementById("perr");
if(loginform.username.value == "") {
userinfo.innerHTML = "用户名错误" ;
return false;
//增加return false;
}
if (loginform.password.value == "") {
passinfo.innerHTML = "密码错误";
return false;
//增加return false;
} }
-->
</script>
</head>
<body>
<form id="loginform" name="loginform" method="post" action="">
<table width="354" height="176" border="0">
<tr>
<td colspan="2">云南大学自习室系统</td>
</tr><tr>
<td width="">用户名
</td><td>
<input type="text" name="username" id="username"/>
</td>
</tr><tr>
<td colspan="2"><div id="uerr"></div></td>
</tr><tr>
<td>密码</td>
<td><input type="password" name="password" id="password"/></td>
</tr><tr>
<td colspan="2"><div id="perr"></div></td>
</tr><tr>
<td><input type="submit" name="Submit" value="登录" onClick=" return validity();"></td>
<td> </td>
</tr>
</table>
</form>
</body>
</html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>云南大学自习室系统</title>
<script type="text/javascript">
<!--
function validity(){
var userinfo=document.getElementById("uerr");
var passinfo=document.getElementById("perr");
if(document.getElementById('username').value == '') {
userinfo.innerHTML = "用户名错误" ;
return false;
//增加return false;
}
if (document.getElementById('password').value == '') {
passinfo.innerHTML = "密码错误";
return false;
//增加return false;
} }
-->
</script>
</head>
<body>
<form id="loginform" name="loginform" method="post" action="">
<table width="354" height="176" border="0">
<tr>
<td colspan="2">云南大学自习室系统</td>
</tr><tr>
<td width="">用户名
</td><td>
<input type="text" name="username" id="username"/>
</td>
</tr><tr>
<td colspan="2"><div id="uerr"></div></td>
</tr><tr>
<td>密码</td>
<td><input type="password" name="password" id="password"/></td>
</tr><tr>
<td colspan="2"><div id="perr"></div></td>
</tr><tr>
<td><input type="submit" name="Submit" value="登录" onClick=" return validity();"></td>
<td> </td>
</tr>
</table>
</form>
</body>
</html>