Question

我正在尝试验证我的用户名字段，并检查用户名是否包含至少6个字母，如果没有，那么我会显示一个弹出窗口，指示相同。但是警报命令似乎不起作用。

以下是代码：

<html>
<head>
<title> Webpage </title>
</head>
<script language="Javascript">
function validate()
{

if (username1.length < 6)
{
alert("Username must be atleast 6 charactrs long, Please Try Again");
}

}


</script>
<body>
<form>
<center>
 <fieldset>
<table cellspacin="5" cellpadding="5" border="0">

<tr>
<td>Username: </td>
<td align="left"><input type=="text" name="username1" maxlength="20" size="20">
</td>
</tr>

<tr>
<td> Password: </td>
<td align = "left"> <input type="text" name="password" maxlength="20" size="20">
</td>
</tr>

<tr>
<td> Please confirm your password: </td>
<td align = "left"> <input type="text" name="password1" maxlength="20"        size="20">
</td>
</tr>

<tr>
<td align="center"><input type="submit" value="Log in" onClick="validate()">
</td>
</tr>
</fieldset>
</table>

</center>
</form>
</body>
</html>

Answer 1

您正在尝试使用name元素属性作为id，这会创建一个全局窗口属性。名称不会这样做，但您可以使用。你也没有得到这个价值，你试图获得元素的长度。

document.getElementsByName('username1')[0].value

Answer 2

答案：我尝试了这种方式：

       <html>
       <head>
      <title> Webpage </title>
     </head>
      <script language="Javascript">
     function validate()
     {

     username2 =form1.username1.value

    if (username2.length < 6)
    {
    alert("Username must be atleast 6 charactrs long, Please Try Again");
    } 

   } 


  </script>
  <body> 
  <form name="form1">
   <center>
  <fieldset>
  <table cellspacin="5" cellpadding="5" border="0">

 <tr>
 <td>Username: </td>
 <td align="left"><input type=="text" name="username1" maxlength="20" size="20">
 </td>
 </tr>

 <tr>
 <td> Password: </td>
 <td align = "left"> <input type="text" name="password" maxlength="20" size="20">
 </td>
 </tr>

 <tr>
 <td> Please confirm your password: </td>
 <td align = "left"> <input type="text" name="password1" maxlength="20" size="20">
 </td>
 </tr>

 <tr>
  <td align="center"><input type="submit" value="Log in"  onClick="validate()">
 </td>
 </tr>
 </fieldset>
 </table>

 </center>
 </form>
 </body>
 </html>

Javascript验证用户名长度

2 个答案: