[removed] Do I need to put this.var for every variable in an object?

Question

In C++, the language I\'m most comfortable with, usually one declares an object like this:

class foo
{
public:
    int bar;
    int getBar() { return bar; }
         


        

Answer 1

function Foo() {
  this.bar = 0;
  this.getBar = function () { return this.bar };
}

When you call the function above with the new keyword - like this...

var foo = new Foo();

... - a few things happen:

1) an object is created
2) the function is executed with the this keyword referencing that object.
3) that object is returned.

foo, then, becomes this object:

{
    bar: 0,
    getBar: function () { return this.bar; }
};

Why not, then, just do this:

var foo = {
    bar: 0,
    getBar: function () { return this.bar; }
};

You would, if it's just that one simple object.

But creating an object with a constructor (that's how it's called) gives us a big advantage in creating multiple of the "same" objects.

See, in javascript, all functions are created with a prototype property [an object], and all objects created with that function (by calling it with the new keyword) are linked to that prototype object. This is why it's so cool - you can store all common methods (and properties, if you wanted to) in the prototype object, and save a lot of memory. This is how it works:

function Foo( bar, bob ) {
   this.bar = bar;
   this.bob = bob;
}

Foo.prototype.calculate = function () {
  // 'this' points not to the 'prototype' object 
  // as you could've expect, but to the objects
  // created by calling Foo with the new keyword.
  // This is what makes it work.
  return this.bar - this.bob;  
};

var foo1 = new Foo(9, 5);
var foo2 = new Foo(13, 3);
var result1 = foo1.calculate();
var result2 = foo2.calculate();

console.log(result1); //logs 4
console.log(result2); //logs 10

That's it!