get size of json object

you dont need to change your JSON format.

replace:

console.log(data.phones.length);

with:

console.log( Object.keys( data.phones ).length ) ;

Consider using underscore.js. It will allow you to check the size i.e. like that:

var data = {one : 1, two : 2, three : 3};
_.size(data);
//=> 3
_.keys(data);
//=> ["one", "two", "three"]
_.keys(data).length;
//=> 3

You can use something like this

var myObject = {'name':'Kasun', 'address':'columbo','age': '29'}

var count = Object.keys(myObject).length;
console.log(count);

Your problem is that your phones object doesn't have a length property (unless you define it somewhere in the JSON that you return) as objects aren't the same as arrays, even when used as associative arrays. If the phones object was an array it would have a length. You have two options (maybe more).

1. Change your JSON structure (assuming this is possible) so that 'phones' becomes

   "phones":[{"number":"XXXXXXXXXX","type":"mobile"},{"number":"XXXXXXXXXX","type":"mobile"}]
   

   (note there is no word-numbered identifier for each phone as they are returned in a 0-indexed array). In this response phones.length will be valid.

2. Iterate through the objects contained within your phones object and count them as you go, e.g.

   var key, count = 0;
   for(key in data.phones) {
     if(data.phones.hasOwnProperty(key)) {
       count++;
     }
   }
   

If you're only targeting new browsers option 2 could look like this