Javascript json returning undefined -

so i'm trying grab data json object through in loop , keeps returning undefined. here code:

router.get('/', function(req, res, next) {   request('https://api.instagram.com/v1/media/popular?client_id=############', function (error, response, body) {     json = json.parse(body);     var popular_tags = [];      (var key in json['data']){       tag = json.stringify(key['tags'])         popular_tags.push(tag)       }     console.log(popular_tags)      res.render('index', {title: body });   }); }); 

this output recieve:

[ undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined,   undefined ] 

however, when try

var popular_tags = []; popular_tags.push(json['data'][0]['tags']) console.log(popular_tags) 

it print out want. suggestions?

change line to

tag = json.stringify(json['data'][key]['tags'])