Add function as method of Array native object (Is it possible to call a function as a method?)

Question

I feel like there's probably something incredibly simple I missed in the MDN docs or something, but I've been digging for a while, and I have no clue.

Is there a way to call a function in a similar way to a method? This is basically what I'm trying to do:

function addItem(itemName, quality, quantity /*, arr*/) {
  arr.push([itemName, quality, quantity]);
}

var someArr = [['item', 1, 1]];

someArr.addItem('someOtherItem', 2, 3);
// someArr === [['item', 1, 1], ['someOtherItem', 2, 3]]

Now, mind you, I'm not trying to make a constructor or define a variable as a function. Furthermore, I am fully aware that I could simply add the array as an argument and call the function as normal. What I'm trying to accomplish is running a function in a way that, when notated as an array method, will affect that array in the specified way. How can I do this? Can I do this at all?

Answer 1

DANGEROUS APPROACH (disclaimer :P):
I do not advocate extending native objects, so the following solution serves only as a reference one way to achieve it but is highly discouraged in practice. See: THE DANGERS OF EXTENDING NATIVE OBJECTS

Array.prototype.addItem = function addItem(itemName, quality, quantity) {
  this.push([itemName, quality, quantity]);
}

var someArr = [['item', 1, 1]];

someArr.addItem('someOtherItem', 2, 3);

console.log(someArr); 
// logs out: [["item", 1, 1], ["someOtherItem", 2, 3]]

The use of this inside the new method with be set to the object that the method is called upon. In the case of this example, this will be the array someArr.

---

A BETTER APPROACH: extend the array instance of someArr with the addItem function (and NOT the native Array object):

var someArr = [['item', 1, 1]];

// set property 'addItem' on someArr to equal named function expression
someArr.addItem = function addItem(itemName, quality, quantity) {
  this.push([itemName, quality, quantity]);
};

someArr.addItem('someOtherItem', 2, 3);

console.log(someArr); 
// logs out: [["item", 1, 1], ["someOtherItem", 2, 3]]