JavaScript 实现的简单表单验证功能完整实例

<!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>www.jb51.net 表单验证</title>
<style type="text/css">
<!--
body,td,th {
  font-size: 12px;
  color: #000000;
}
body {
  background-color: #CCCCCC;
  margin-left: 0px;
  margin-top: 0px;
}
a {
  font-size: 12px;
  color: #666600;
}
a:link {
  text-decoration: none;
}
a:visited {
  text-decoration: none;
  color: #000099;
}
a:hover {
  text-decoration: underline;
  color: #6633FF;
}
a:active {
  text-decoration: none;
  color: #00FF00;
}
-->
</style>
  <script type="text/javascript">
    function checkusername()
    {
      var myform = document.getElementById("form1");
      var username = myform.username.value.length;
      if(username < 1||username>12)
      {
        errusername.innerHTML = "<font color='red'>用户名不符合要求</font>";
        return false;
      }else{
        errusername.innerHTML = "<font color='green'>用户名符合要求</font>";
        return true;
      }
    }
    function checkage()
    {
      var myform = document.getElementById("form1");
      var age = myform.age.value;
      if(age != parseInt(age))
      {
        errage.innerHTML = "<font color='red'>年龄不符合要求</font>";
        return false;
      }else{
        errage.innerHTML = "<font color='green'>年龄符合要求</font>";
        return true;
      }
    }
    function checkemail()
    {
      var myform = document.getElementById("form1");
      var mail=/^[A-Za-z0-9_-]+@[a-zA-Z0-9_-]+(\.[a-zA-Z0-9_-]+)+$/;
      if(!mail.test(myform.email.value))
      {  
        erremail.innerHTML = "<font color='red'>email不符合要求</font>";
        return false;
      }else{
        erremail.innerHTML = "<font color='green'>email符合要求</font>";
        return true;
      }
    }
    function checkform()
    {
      checkusername();checkage();checkemail();
      if(checkusername()&&checkage()&&checkemail())
      {
        return true;  
      }else{
        return false;
      }
    }
  </script>
</head>
<body alink="center">
 <form id="form1" name="form1" method="post" action="ttt.jsp" onsubmit="return checkform()">
<table width="777" border="0" cellpadding="1" cellspacing="1">
 <tr>
  <td colspan="3" ><div align="center">请输入你的注册信息</div></td>
 </tr>
 <tr>
  <td width="250" ><div align="right" >请输入你的用户名：</div></td>
  <td width="250"><div align="center">
     <input type="text" name="username" onblur="checkusername()" />  
   </div></td>
  <td><div id="errusername" align="center"></div></td>
 </tr>
 <tr>
  <td width="250"><div align="right">请输入你的年龄：</div></td>
  <td width="250"><div align="center" >
   <label>
   <input type="text" name="age" onblur="checkage()"/>
   </label>
  </div></td>
   <td><div align="center" id="errage"></div></td>
 </tr>
 <tr>
  <td width="250"><div align="right" >请输入你的EMAIL:</div></td>
  <td width="250"><div align="center" >
   <label>
   <input type="text" name="email" onblur="checkemail()" />
   </label>
  </div></td>
   <td><div align="center" id="erremail"></div></td>
 </tr>
 <tr>
  <td><div align="right">
   <label>
   <input type="submit" name="Submit" value="提交" />
   </label>
  </div></td>
   <td><div align="center">
    <label>
    <input type="reset" name="Submit2" value="重置" />
    </label>
   </div></td>
  <td><div align="center"></div></td>
 </tr>
</table>
 </form>
</body>
</html>