Use object property for iteration

Question

it is possible to use a object property for a "for in"-Iteration in JavaScript?

I want write a Bag-Class like this:

var Bag = function () {
  this.elements = {};
}

Bag.prototype.add = function (key, value) {
  this.elements[key] = value;
};

// other methods ...

Now i want use objects of this class in a for in iteration:

for (var key in myBag) {
  console.log(myBag[key]); // or myBag.get(key);
}

It is possible to do this without a helper method like var key in myBag.getAll()?

Answer 1

You could add the key/value pairs to the instance itself, and create the method as non-enumerable, for example:

function Bag() {
}

Object.defineProperty(Bag.prototype, 'add', {
  enumerable: false,
  value: function(k, v) {
    this[k] = v
  }
})

var bag = new Bag
bag.add('a',1)
bag.add('b',2)
bag.add('c',3)

for (var k in bag)
  console.log(k)
//^ a
//  b
//  c

Note, that you could also declare the method normally and always loop with hasOwnProperty check:

for (var k in bag)
  if (bag.hasOwnProperty(k))
    console.log(k)

Or another alternative:

Object.keys(bag).forEach(function(k) {
  console.log(k)
})