Accessing Javascript object prototype

This question already has an answer here:

How does JavaScript .prototype work? 21 answers

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You do have access to the prototype property, but it is only present on Function s.

var car = {
    Make: 'Nissan',
    Model: 'Altima'
}; 

This is the same as:

var car = new Object();
car.Make = 'Nissan';
car.Model = 'Altima'; 

So, car.__proto__ === Object.prototype .

And car.prototype === undefined as the prototype property is only present on Function s (as I already said).

function Car() {
    this.Make = 'NISSAN';
    this.Model = 'Atlanta';
}

Here Car.prototype points to an instance of Object because Car is a function and when function declarations are evaluated their prototype is set to an instance of Object .

Car.prototype.Year = 2014; //all Car *instances* will have a Year property set to 2014 on their prototype chain.

var c = new Car(); //create an instance
console.log(c.Year); //2014

Overriding a method present on the prototype chain for an object is as simple as creating a corresponding method on the object:

var myObject = new Object();
myObject.toLocaleString = function() {
  //my own implementation
};

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You probably want to modify the constructor function prototype:

function Car(year, make, model) {
  this.year  = year;
  this.make  = make;
  this.model = model;
}

Car.prototype.toLocaleString = function() {
  return [this.year, this.make, this.model].join(' ');
};

var civic = new Car(2014, 'Honda', 'Civic');
civic.toLocaleString(); // => "2014 Honda Civic"

This MDN article on Object.prototype might be helpful.

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