Understanding JavaScript Prototypes.

모든 Object Prototype 을 갖는다.

var a = {};

//Firefox 3.6 and Chrome 5
Object.getPrototypeOf(a); //[object Object]

//Firefox 3.6, Chrome 5 and Safari 4
a.__proto__; //[object Object]

//all browsers
a.constructor.prototype; //[object Object]


 Prototype 상속 받아 사용 할수 있다 

//unusual case and does not work in IE
var a = {};
a.__proto__ = Array.prototype;
a.length; //0


//function will never be a constructor but it has a prototype property anyway
Math.max.prototype; //[object Object]

//function intended to be a constructor has a prototype too
var A = function(name) {
	this.name = name;
}
A.prototype; //[object Object]

//Math is not a function so no prototype property
Math.prototype; //null

예제

//생성자 

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

var A = function(name) {
    this.name = name;
}

var a = new A('alpha');
a.name; //'alpha'

A.prototype.x = 23;

a.x; //23

prototype 활용

String.prototype.times = function(count) {
    return count < 1 ? '' : new Array(count + 1).join(this);
}

"hello!".times(3); //"hello!hello!hello!";
"please...".times(6); //"please...please...please...please...please...please..."