注册示例

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <title>Title</title>
 6 </head>
 7 <body>
 8 <form action="" id="Form">
 9     用户名：<input type="text" name="username" class="con" mark="用户名"><br>
10     密码&nbsp;&nbsp;&nbsp;：<input type="password" name="pwd" class="con" mark="密码"><br>
11     <input type="submit" value="submit">
12 
13 
14 </form>
15 
16 <script src="jquery-3.2.1.js"></script>
17 <script>
18      $("#Form :submit").click(function () {
19          var flag=true;
20          $("#Form .con").each(function () {
21              if ($(this).val().trim().length==0){
22                  var span=$("<span>");
23                  var mark=$(this).attr("mark");
24                  span.text(mark+"不能为空");
25 
26                  $(this).after(span);
27                  flag=false;
28                  return false;
29              };
30 
31          });
32          return flag
33       });
34 </script>
35 </body>
36 </html>