customIterator.js

let iterable = {
    0: 'a',
    1: 'b',
    2: 'c',
    length: 3,
    [Symbol.iterator]() {
	  var keys = Object.keys(this).sort();
	  var index = 0;
  
	  return {
	    next: function () {
	      return {
	        value: keys[index], done: (index++ >= keys.length-1)
	      };
	    }
	  }
	}
};


for (let item of iterable) {
    console.log(item); 
}