//while循环实现 function calNum(n) {    var product = 1;    while(n > 1){
   //1*5*4*3*2，1*n*(n-1)*(n-2)*...*2        product *= n;        n--;    }    return product;}console.log(calNum(5))

 

//js实现阶乘	function calNum(n){		var a = 1, str = '1*';		for (var i = 2; i <= n; i++) {			str += i + '*';			a *= i;		}		str = str.substr(0,str.length-1);		return str + '=' +a;	}	console.log(calNum(5));       //打印结果为：1*2*3*4*5=120