JavaScript Object Prototypes

All JavaScript objects inherit properties and methods from a prototype.

Example

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}
var myFather = new Person("John", "Doe", 50, "blue");
var myMother = new Person("Sally", "Rally", 48, "green");

you can not add a new property to an existing object constructor like this : Person.nationality = "English"; To add a new property to a constructor, you must add it to the constructor function:

Example

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
  this.nationality = "English";
}

Prototype Inheritance

All JavaScript objects inherit properties and methods from a prototype:
• Date objects inherit from Date.prototype
• Array objects inherit from Array.prototype
• Person objects inherit from Person.prototype

The Object.prototype is on the top of the prototype inheritance chain: Date objects, Array objects, and Person objects inherit from Object.prototype.

Adding Properties and Methods to Objects

The JavaScript prototype property allows you to add new properties to object constructors:

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}
Person.prototype.nationality = "English";

The JavaScript prototype property also allows you to add new methods to objects constructors:

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}
Person.prototype.name = function() {
  return this.firstName + " " + this.lastName;
};