How to “properly” create a custom object in JavaScript?

Question

I wonder about what the best way is to create an JavaScript object that has properties and methods.

I have seen examples where the person used var self = this<

Answer 1

Closure is versatile. bobince has well summarized the prototype vs. closure approaches when creating objects. However you can mimic some aspects of OOP using closure in a functional programming way. Remember functions are objects in JavaScript; so use function as object in a different way.

Here is an example of closure:

function outer(outerArg) {
    return inner(innerArg) {
        return innerArg + outerArg; //the scope chain is composed of innerArg and outerArg from the outer context 
    }
}

A while ago I came across the Mozilla's article on Closure. Here is what jump at my eyes: "A closure lets you associate some data (the environment) with a function that operates on that data. This has obvious parallels to object oriented programming, where objects allow us to associate some data (the object's properties) with one or more methods". It was the very first time I read a parallelism between closure and classic OOP with no reference to prototype.

How?

Suppose you want to calculate the VAT of some items. The VAT is likely to stay stable during the lifetime of an application. One way to do it in OOP (pseudo code):

public class Calculator {
    public property VAT { get; private set; }
    public Calculator(int vat) {
        this.VAT = vat;
    }
    public int Calculate(int price) {
        return price * this.VAT;
    }
}

Basically you pass a VAT value into your constructor and your calculate method can operate upon it via closure. Now instead of using a class/constructor, pass your VAT as an argument into a function. Because the only stuff you are interested in is the calculation itself, returns a new function, which is the calculate method:

function calculator(vat) {
    return function(item) {
        return item * vat;
    }
}
var calculate = calculator(1.10);
var jsBook = 100; //100$
calculate(jsBook); //110

In your project identify top-level values that are good candidate of what VAT is for calculation. As a rule of thumb whenever you pass the same arguments on and on, there is a way to improve it using closure. No need to create traditional objects.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Closures