//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))
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));
