表单验证的两种方法：
一、onsubmit验证：
<script language="javascript">
function CheckPost () {
if (addForm.user.value == "") {
alert("请填写用户名！");
addForm.username.focus();
return false;
}
if (addForm.title.value.length < 5) {
alert("标题不能少于5个字符！");
addForm.title.focus();
return false;
}
return true;
}
</script>
<form action="test.php" method="post" name="addForm" onsubmit="return CheckPost();">
<p>用户:<input type="text" size="10" name="user" maxlength="20"/></p>
<p>标题:<input type="text" name="title" maxlength="50"/></p>
<p>内容:<textarea name="content" rows="8" cols="30"></textarea></p>
<p><input type="submit" name="submit" onclick="SendForm();" value="发表留言"/></p>
</form>
<?php
if($_POST['submit']) {
echo "<script language=\"javascript\">alert('提交成功！');history.go(-1);</script>";
}
?>二、onclick验证：
<script language="javascript">
function SendForm () {
if(CheckPost()) {
document.addForm.submit();
}
}
function CheckPost () {
if (addForm.user.value == "") {
alert("请填写用户名！");
addForm.username.focus();
return false;
}
if (addForm.title.value.length < 5) {
alert("标题不能少于5个字符！");
addForm.title.focus();
return false;
}
return true;
}
</script>
