How to use ajax to receive json data in ThinkPHP, thinkphpjson_PHP tutorial

function ajax(id,pic){
//Since ThinkPHP does not parse ThinkPHP constants in JavaScript, they need to be defined here first.
var URL='__URL__';
          $.ajax({
​​​​​​ url: URL+'/returnAjax/id/'+id,//Submit the URL for access
            type: 'GET', // Submission method
                  dataType: 'text', //The type of content returned, since the PHP file is echoed directly, then here is text
            timeout: 1000, // timeout time
​​​​​​ error: function(){ //If an error occurs, execute the function
alert('Error loading XML document');
            },
Success: function(data){
                       //alert(data);//If successful, pop up the data
                    writeHtml(data,pic);
            }
        });
}
function writeHtml(data,pic){
var product = eval('(' + data + ')'); //It can be converted into a json object even without introducing json.js
//alert($("#cate_pic").attr("src"));
$("#cate_pic").attr("src","../images/"+pic);
$("#product_pic").attr("src","../Attachments/product/"+product.attachpath+"/"+product.attachthumb);
$("#product_subject").html(product.subject);
$("#product_content").html(product.content);
}

public function returnAjax(){
         $id = $_GET['id'];
$Product=D('Product')->where('id='.$id)->find();
//Return a data set in json format
echo json_encode($Product);
//print_r(json_encode($Product));
}

{
"id":"9",
"userid":"1",
"cid":"10",
"cid":"10",
"subject":"1111",
"color":"",
"spec":"",
"size":"",
"keywords":"",
"content":"

1111

",
"meno":"1111",
"attachpath":"200903",
"attachment":"49d1d86e68d31.png",
"attachthumb":"49d1d86e68d31_thumb.png"
}