Javascript prototype example (Which you've seen 100's of times)

gistfile1.js

//Constructor. <em>this</em> is returned as new object and its
// internal [[prototype]] property will be set to the constructor's
// default prototype property.
//
var Circle = function(radius)
{
    this.radius = radius;
    // Next line is implicit, added for illustration only.
    //
    // this.__proto__ = Circle.prototype;
}

// augment Circle's default prototype property thereby augmenting
// the prototype of each generated instance
//
Circle.prototype.area = function()
{
   return Math.PI*this.radius*this.radius;
}

// create two instances of a circle and make each leverage
// the common prototype
//
var a = new Circle(3), b = new Circle(4);
a.area().toFixed(2); // 28.27
b.area().toFixed(2); // 50.27