All JavaScript objects inherit properties and methods from a prototype.
In the previous chapter we learned how to use an object constructor:
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"); We also learned that you can not add a new property to an existing object constructor:
Example #
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:
Dateobjects inherit fromDate.prototypeArrayobjects inherit fromArray.prototypePersonobjects inherit fromPerson.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 #
Sometimes you want to add new properties (or methods) to all existing objects of a given type.
Sometimes you want to add new properties (or methods) to an object constructor.
Using the prototype Property #
The JavaScript prototype property allows you to add new properties to object constructors:
Example #
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:
Example #
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;
}; Only modify your own prototypes. Never modify the prototypes of standard JavaScript objects.
