How to add json callback to php file?

Created a javascript widget. Had problems with same origin policy. I added the callback to the php file like this:

 var jsonp_url = "http://www.example.com/widget/data.php?json_callback=?";
        $.getJSON(jsonp_url, function(data) {



            for (var i=0;i<data.length-1; i++) {

            var li = document.createElement("li");
            li.setAttribute("class", "top-coupon");


            var coupon_details = document.createElement("div");
            coupon_details.setAttribute("class", "coupon-details");
            coupon_details.innerHTML=data[i].coupon_name;

            li.appendChild(coupon_details);


            var image = document.createElement("img");
            image.setAttribute("src", "http://static.example.com/images/logos/" + data[i].logo_image);
            image.setAttribute("class","logo-image");
            image.setAttribute("width","40px");
            image.setAttribute("height","40px");


            li.appendChild(image);




           ul.appendChild(li);

            }
        });
        widget.appendChild(ul);

Now I don't know how to add the callback to the data.php file. This is what I've tried:

        while($info = mysql_fetch_array($result)){

        $json = array();    
    $json['coupon_name'] = $info['label'] ;
    $json['retailer_name'] = $info['name'] ;
    $json['logo_image'] = $info开发者_StackOverflow社区['logo_image'];
    $json['permalink'] = $info['permalink'];
    $data[] = $json;
            }
            $data2 = json_encode($data); 
            echo $data2; 
            echo $_GET['json_callback'] . '(' . $data2 . ');';

Remove echo $data2; - currently your page generates invalid javascript

Javascript:

$.getJSON("http://www.example.com/widget/data.php",function(data){
    // data is your JSON Object
});

PHP:

$data = array();
while($info = mysql_fetch_array($result)) $data[]=$info;
echo json_encode($data);