javascript継承小例(動態原型方法)

function Polygon(iSides){
	this.sides = iSides;
	
	if(typeof Polygon._initialized == "undefined") {
	
		Polygon.prototype.getArea = function(){
			
			return 0;
		};
		
		Polygon._initialized = true;
	}
}

function Triangle(iBase , iHeight){

	Polygon.call(this , 3);
	this.base = iBase;
	this.height = iHeight;
	
	// Triangle._initialized   Triangle    （ java        ）
	if(typeof Triangle._initialized == "undefined"){
		
		//    ，   prototype       ，     prototype，           ，         ，  prototype                   ，  alert(triangle.getArea())   。
		//Triangle.prototype = new Polygon();
		Triangle.prototype.getArea = function(){
			
			return 0.5 * this.base * this.height;
		}
		
		Triangle._initialized = true;
	}
}

function myload(){
	//           ，Triangle._initialized    ，    
	//alert(triangle._initialized);
	var triangle = new Triangle(12 , 4);
	//alert(triangle._initialized);
	
	alert(triangle.sides);
	alert(triangle.getArea());
}