JS——阶乘的三种做法（正向逆向递归）

一、正向求阶乘

    function factorial(n) {var product = 1, i = 2;while (i <= n) {product *= i;}return product;}alert(factorial(4));

 

二、逆向求阶乘

    function factorial(n) {var product = 1;while (n > 1) {product *= n;n--;}return product;}alert(factorial(4));

三、递归求阶乘

    function factorial(n) {if (n <= 1) {return 1;} else {return n * factorial(n - 1);}}alert(factorial(4));