js 遞歸 best practice

知識點.

JS 函數內部有兩個特殊對象 arguments 和 this.
arguments 對象中有一個屬性 callee. 該屬性是一個指針，指向擁有這個arguments對象的函數。

例子.

function getJ(num)
{//Function expression 1.
	if(num <= 1){
		return 1;
	}else{
		return num * getJ(num-1); //getJ ponit to Function expression 2. 
					  //so it will cause a bug when you use jCoyp but redefine the getJ.
	}
}
var jCoyp = getJ;	//jCoyp point to Function expression.
//this make getJ point to a new Function expression 2.
getJ = function()
{//Function expression 2.
	return 0;
}
console.log('getJ-------->'+getJ(5));		//result 0 			getJ ponit to Function expression 2.
console.log('jCoyp------->'+jCoyp(5));		//result 0




function getJR(num)
{//Function expression 3.
	if(num <= 1){
		return 1;
	}else{
		return num * arguments.callee(num-1); //arguments.callee point to Function expression 3.
	}
}
var jrCoyp = getJR;
getJR = function()
{//Function expression 4.
	return 0;
}
console.log('getJR-------->'+getJR(5));			//0
console.log('jrCoyp------->'+jrCoyp(5));		//120