Javascript 减少功能后不起作用？

Question

不太确定我哪里出错了，期望通过将 5 变成 [1,2,3,4,5] 的字符串来对 5 (1*2*3*4*5 = 120) 进行因式分解，并且然后使用 reduce 将字符串全部相乘。当我运行代码时，它只会给我 [1,2,3,4,5]...

 var arr = [];

function factorialize(num) {

 for (var i = 1; i <= num; i++) {
  arr.push(i);
}
  return arr;
}

var factors = 0;

factors = arr.reduce(function(previousVal, currentVal) {
  return previousVal * currentVal;
}, 0); // Expecting 120, instead result = [1,2,3,4,5]

factorialize(5);

请原谅这条漫长的路——我第一周的 Javascript!

Answer 1

arr 为空，应该先给它因式分解的结果数组，并且应该乘而不是加，并且乘时起始值为1而不是0:

var arr = [];

function factorialize(num) {
  for (var i = 1; i <= num; i++) {
    arr.push(i);
  }
  return arr;
}

arr = factorialize(5); // give it the value

var factors = arr.reduce(function(previousVal, currentVal) {
  return previousVal * currentVal; // multiply, don't add
}, 1); // start with 1 when multiplying

console.log(arr);
console.log(factors);

如果您只想计算阶乘:

function factorial(num) {
  var res = 1;
  for (var i = 2; i <= num; i++) {
    res *= i;
  }
  return res;
}
console.log('factorial(5) = ' + factorial(5));
console.log('factorial(10) = ' + factorial(10));