帮我把代码看一下求解决else不存在可以注册不能显示

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
    <title>用户注册 </title>    <link href="css/styles.css" rel="stylesheet" type="text/css" media="all"/>    <script type="text/javascript" src="js/jquery.min.js"></script></head>
<body><div class="message warning">
    <div class="inset">
        <div class="login-head">
            <h1>用户注册</h1>            <div class="alert-close"></div>
        </div>        <form method="post" action="zhuc.php?action=doreg">
            <ul>
                <li><input type="text" class="text" name="username" id="name" value="用户名"></li>
                <li><p id="show"></p></li>
                <li><input type="password" name="password" value=""/> <a href="#" class="icon lock"></a></li>
                <li><input type="password" name="rpwd" value=""/> <a href="#" class="icon lock"></a></li>
            </ul>            <div class="submit">
                <input type="submit"  value="注册">
                <h4><a href="#">忘记密码?</a></h4>                <div class="clear"></div>
            </div>
        </form>
    </div>
</div><!--- footer --->
<div class="footer">
    <p>Copyright &copy; 2010-2016.<a href="http://localhost/myblog/index.php">我的网站</a></p>
</div>
<script>
    document.getElementById('name').onblur=function(){
        var request=new XMLHttpRequest();
        request.open('get','zhuc.php?action=check&name='+document.getElementById('name').value);
        request.send();
        request.onreadystatechange=function(){
            if(request.readyState===4 && request.status===200){
                var text=request.responseText;
                if(text='已存在'){
                    document.getElementById('show').innerHTML=text;                }else{
                    document.getElementById('show').innerHTML=text;
                }
            }
        }
    }
</script></body>
</html>
php代码：
<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2016/11/7
 * Time: 9:50
 */
include "chuangj.php";
$action=isset($_GET['action'])?$_GET['action']:'zzc';
if($action=='zzc'){
    include_once"template/reg.html";
}elseif($action=='doreg'){
    $name=addslashes($_POST['username']);
    if(isset($name)){
        $sql="select yh_name from yh WHERE yh_name='$name'";
        $yhq=$df->query($sql)->fetch();
        if(!$yhq){
            $rpwd=addslashes($_POST['rpwd']);
            $pwd=addslashes($_POST['password']);
            if($pwd===$rpwd){
                $sq="insert into yh VALUES (NULL ,'$name','$pwd','')";
                $yhk=$df->exec($sq);
                if($yhk){
                    echo "<script>location.href='dll.php'</script>";
                }else{
                    echo "<script>location.href='zhuc.php'</script>";
                }
            }else{
                echo "<script>location.href='zhuc.php'</script>";
            }
        }else{
            echo "<script>location.href='zhuc.php'</script>";
        }
    }else{
        echo "<script>location.href='zhuc.php'</script>";
    }
}elseif($action=='check'){
    $name=$_GET['name'];
    $sql="select * from yh WHERE yh_name='$name'";
    $data=$df->query($sql)->fetch();
    if($data){
        echo "已存在";
    }
    else{
        echo "不存在可以注册";
    }
}