用户名不能为空

1 var regex = /\s+/g;

1 string.replace(regex,‘‘);

1 function regexEmpty(obj){
2      obj.value = obj.value.replace(regex,‘‘);
3 }

1 < div class= "main">
2            < input id= "userName" type= "text" placeholder= "请输入用户名" >
3            < input id= "rule" type= "button" value= "验证">
4 </ div>

1 html,body ,div, input{margin :0; padding:0 ;}
2             .main{width :400px ;height: auto;padding :0 15px; text-align:center; }
3             .main input{width :100% ;height: 35px; border:none ;margin-top: 20px; border-radius:5 px;}
4            input[type ="text"] {text-align: left;padding-left :15px ;box-sizing: border-box;border :1px solid green; }
5             input[type ="button"] {width: 50%; background:green; }

 1 var userName = document.getElementById(‘userName‘ ),
 2                 rule  = document.getElementById( ‘rule‘),
 3                 deleteEmpty = null,
 4                 regex    = /\s+/g;
 5             deleteEmpty = function (obj){
 6                 obj.value = obj.value.replace(regex,‘‘ );
 7                  if(! obj.value){
 8                      alert( ‘用户名不能为空‘ );
 9                 } else{
10                         alert(‘pass‘);
11                 }
12            }
13            rule. onclick = function (){
14                 deleteEmpty(userName);
15 };