第一种：

 

<script type="text/javascript">
         function check(form) {
          
          if(form.userId.value=='') {
                alert("请输入用户帐号!");
                form.userId.focus();
                return false;
           }
       if(form.password.value==''){
                alert("请输入登录密码!");
                form.password.focus();
                return false;
         }
         return true;
         }
</script>

<form action="login.do?act=login" method="post">

用户帐号
  <input type=text name="userId" size="18" value="" >

<br>

 登录密码     

<input type="password" name="password" size="19" value=""/>     

 <input type=submit name="submit1" value="登陆" onclick="return check(this.form)"> 

</form> 

 

 

 第二种

 

 

<script type="text/javascript">
         function check(form) {
          
          if(form.userId.value=='') {
                alert("请输入用户帐号!");
                form.userId.focus();
                return false;
           }
       if(form.password.value==''){
                alert("请输入登录密码!");
                form.password.focus();
                return false;
         }
         return true;
         }
</script>

<form action="login.do?act=login" method="post" onsubmit="return check(this)">

用户帐号
  <input type=text name="userId" size="18" value="" >

<br>

 登录密码     

<input type="password" name="password" size="19" value=""/>     

 <input type=submit name="submit1" value="登陆"> 

</form>        

 

 

 

第三种：

 

<script type="text/javascript">
         function check(form) {
          
          if(form.userId.value=='') {
                alert("请输入用户帐号!");
                form.userId.focus();
                return false;
           }
       if(form.password.value==''){
                alert("请输入登录密码!");
                form.password.focus();
                return false;
         }
        

          document.myform.submit();

}
</script>

<form action="login.do?act=login" name="myform" method="post">

用户帐号
  <input type=text name="userId" size="18" value="" >

<br>

 登录密码     

<input type="password" name="password" size="19" value=""/>     

<input type=button name="submit1" value="登陆" onclick="check(this.form)"> 

</form>