Accessing Javascript object prototype [duplicate]

Question

As I understand, in JavaScript every object has a prototype and it exposes some default properties. I have the following code where I'm trying to set the Year property of two objects through prototype. But both the calls are failing.

How can I override toLocalString() for any object if I don't have access to the prototype? Please note that the following code is to test on the prototype property, but my intention is to override the toLocalString() method.

var car = {     Make: 'Nissan',     Model: 'Altima' };  car.Year = 2014; alert(car.Year);  alert(car.prototype); // returns undefined  car.prototype.Year = 2014; // Javascript error  // --------------  function Car() {     this.Make = 'NISSAN';     this.Model = 'Atlanta'; }  var v = new Car(); v.prototype.Year = 2014; // JavaScript error alert(v.prototype); 

Answer 1

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

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 Functions (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 }; 

Answer 2

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.