//引入jQuery
<script src="js/jquery-3.2.1.min.js" type="text/javascript" charset="utf-8"></script>
//表單信息
<form action="" method="post">
<input type="text" id="tel">
<span style="color:red;display: none;">手機號不能重複</span> <!-- 驗證顯示 -->
</form>
//ajax驗證
<script type="text/javascript">
$(document).ready(function(){
$("#tel").change( function() {
var phone=$("#tel").val();
$.post('active/check_phone',{//後臺接口
phone:phone
},function(data){
if(data==1){
$("span").css("display","block");
}
if(data==0){
$("apan").css("display","none");
}
})
})
});
</script>