stringify({ data: { hello: 'world', with: { nested: 'objects' } } })

{
  "data": {
    "hello": "world",
    "with": {
      "nested": "objects"
    }
  }
}

function stringify(object, indentation) {
  if (typeof indentation === 'undefined') {
    indentation = 0;
  }

  var items = [];

  for (var key in object) {
    if (object.hasOwnProperty(key)) {
      var value;

      switch (typeof object[key]) {
        case 'object':
          var type = Object.prototype.toString.call(object[key]);

          switch (type) {
            case '[object Null]':
              value = 'null';
              break;

            case '[object Array]':
            case '[object Object]':
              value = stringify(object[key], indentation + 2);
              break;

            default:
              value = type;
          }
          break;

        case 'string':
          value = '"' + object[key] + '"'
          break;

        default:
          value = object[key];
      }

      items.push(Array(indentation + 3).join(' ') + '"' + key + '": ' + value);
    }
  }

  return '{n'
         + items.join(',n') + 'n'
         + Array(indentation + 1).join(' ') + '}';
}

// Example:
console.log(stringify({ data: { hello: 'world', with: { nested: 'objects' } } }));