Javascript this keyword inside functions

Question

I am trying to understand internals of Javascript. I have some misunderstanding of this keyword. Everywhere stated that this keyword is reference to the object that invokes function.

But as far as I know function is an object as well.
So consider this example

var car = {
  brand: "Nissan",
  getBrand: function(){
    var closure = function(){
      console.log(this.brand);
      console.log(this);
    };
    return closure();
  }
};

car.getBrand();  

Why does this reference inside closure point to the global object instead of getBrand wrapping function ? Again everything is object in javascript, so I cannot understand this behavior.

Please explain this from internals perspective.

Thanks

Answer 1

Because value of this is determined by how function is called..closure is called with no reference of context and global context is window(in Browser)

Use Function.prototype.call to specify this context while function is invoked

var car = {
  brand: "Nissan",
  getBrand: function() {
    var closure = function() {
      console.log(this.brand);
      console.log(this);
    };
    return closure.call(this);
  }
};

car.getBrand();