CODEWITHSUNDEEP
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ray smith
ray smith

Reputation: 380

Javascript json returning undefined

So I'm trying to grab some data from a json object through a for in loop and it keeps returning undefined. Here is my 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 = [];

    for (var key in json['data']){
      tag = JSON.stringify(key['tags'])
        popular_tags.push(tag)  
    }
    console.log(popular_tags)

    res.render('index', {title: body });
  });
});

This is the output I recieve:

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

However, when I try 

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

It will print out what I want. Any suggestions?

Upvotes: 0

Views: 344

Answers (2)

Amadan
Amadan

Reputation: 198466

When you say

for (var key in json['data'])

the key is iterating through the attribute names of the object json.data, and is thus a string. Thus, key['tags'] is undefined as strings generally don't have an attribute tags. Things snowball from there.

The general idiom is:

for (var key in json.data) {
  if (json.data.hasOwnProperty(key) {
    var item = json.data[key];
    // ...
  }
}

The hasOwnProperty thing is the protection against someone injecting something in a prototype of whatever you're iterating. For example, if someone did something silly like Object.prototype.breakAllCode = true, "breakAllCode" would show up as a key on whatever you were iterating.

Upvotes: 1

zs2020
zs2020

Reputation: 54543

Change the line to

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

Upvotes: 1

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