// This example is from the book _JavaScript: The Definitive Guide_.    
// Written by David Flanagan.  Copyright (c) 1996 O'Reilly & Associates.
// This example is provided WITHOUT WARRANTY either expressed or implied.
// You may study, use, modify, and distribute it for any purpose.        

// First, define some functions that will be used as methods
function Rectangle_area() { return this.width * this.height; }
function Rectangle_perimeter() { return 2*this.width + 2*this.height; }
function Rectangle_set_size(w,h) { this.width =index.html w; this.height = h; }
function Rectangle_enlarge() { this.width *= 2; this.height *= 2; }
function Rectangle_shrink() { this.width /= 2; this.height /= 2; }

// Then define a constructor method for our Rectangle objects.
// The constructor initializes properties, and also assigns methods.
function Rectangle(w, h) 
{
    // initialize object properties
    this.width = w;
    this.height = h;

    // define methods for the object
    this.area = Rectangle_area;
    this.perimeter = Rectangle_perimeter;
    this.set_size = Rectangle_set_size;
    this.enlarge = Rectangle_enlarge;
    this.shrink = Rectangle_shrink;
}

// Now, when we create a rectangle, we can immediately invoke methods on it:
r = new Rectangle(2,2);
a = r.area();
r.enlarge();
p = r.perimeter();