Constructor

A constructor is a function that instantiates a particular type of Object. You invoke a constructor with the new keyword. Here are a few examples of constructors with built-in JavaScript objects and custom objects.

Constructor Examples

// Creates a generic object.
var myObject = new Object();
// Creates a Date object.
var myBirthday = new Date(1961, 5, 10);
// Creates a user defined object.
var myCar = new Car();

The constructor function contains the this keyword, which is a reference to a newly created empty object. It initializes the new object by creating properties and giving them initial values. The constructor returns a reference to the object it constructed.

[full_width] Writing Constructors

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You can create objects using the new operator in conjunction with predefined constructor functions such as Object(), Date(), and Function(). You can also create custom constructor functions that define a set of properties and methods. Here is an example of a custom constructor.

function Circle (xPoint, yPoint, radius) {
    this.x = xPoint;  // The x component of the center of the circle.
    this.y = yPoint;  // The y component of the center of the circle.
    this.r = radius;  // The radius of the circle.
}