使用Jquery的Ajax实现用户名实时认证

 <form id="login" name = "login">
        <div class="row justify-content-md-center">
            <div class="col col-lg-4">
                <div class="form-group">
                    <label for="username">用户名:</label>
                    <input type="text" name="username" id="username" class="form-control" placeholder="username">
                    <p style="color: red" id = "wrong"></p>
                </div>
            </div>
            <div class="col col-lg-4">
                <div class="form-group">
                    <label for="usernames">密码:</label>
                    <input type="password" name="password" id="password" class="form-control" placeholder="password">
                </div>
            </div>
        </div>
        <div class="row justify-content-md-center">
            <div class="col col-lg-3">
                <div class="form-group">
                    <label for="name">姓名:</label>
                    <input type="text" name="name" id="name" class="form-control" placeholder="username">
                </div>
            </div>

            <div class="col col-lg-2">
                <div class="form-group">
                    <label for="phone">电话:</label>
                    <input type="text" name="phone" id="phone" class="form-control" placeholder="username">
                </div>
            </div>

            <div class="col col-lg-3">
                <div class="form-group">
                    <label for="address">地址:</label>
                    <input type="text" name="address" id="address" class="form-control" placeholder="username">
                </div>
            </div>

        </div>

        <div class="row justify-content-md-center">
             <div class="col col-lg-2">
                <button type="button" class="btn btn-primary" onclick="checkLogin()">register</button>
            </div>
            <div class="col col-lg-1">
                <button type="reset" class="btn btn-primary">reset</button>
            </div>
        </div>
    </form>

<script type="text/javascript">
    var flag;
	$(function() {
        var username;
	 	$("input").keyup(function(){
            username = $("#username").val();

            $.ajax({
                method:‘POST‘,
                async:false,
                url:‘http://localhost:8080/NewTaobao/register‘,
                data:{username:username},
                success:function(data){
                   if(data ==‘faild‘){
                        flag = false;
                   }else{
                	   flag = true;
                   }
                },
                error:function(){
                    alert("连接失败");
                }
            });
           
            if(flag==false){
            	 $("#wrong").text("用户名已经存在");	
            }
            else{
            	 $("#wrong").text("");	
            }
        });
});