"Js函数顶部计算阶乘不起作用"

Question

I was doing this challenge from coderbyte where you have to make a function that calculate the factorial of a given number, this is my not so working solution.

function firstFactorial(num) { 

  for (var i = num; i == 1; i--) {
      num = num * i;
  }
  return num;     
}

It just returns whatever number i pass in as an argument, and i'm trying to understand what's wrong. Is it something to do with the loop or is it something with the variable scope ?

Answer 1

1. i == 1 is wired in loop condition it will always be false for all number except 1.So it will always return the same number as result.

2. i = num should be i = num-1 to get correct factorial.

 function FirstFactorial(num) { for(var i = num-1; i >= 1; i--){ num = num * i; } return num; } console.log( FirstFactorial(5)) 

Answer 2

Your for loop was a bit messed up. Now it should work.

  function factorial(num){ for(var i = num - 1; i > 0; i--){ num *= i; } return num; } console.log(factorial(5)); 

Answer 3

Your problem is that you have a loop condition i == 1 . For factorials, it should be i >= 1 , or i > 1 depending on what algorithm you use. My take on a factorial function would be:

function calculate(factorial) {
    var newFactorial = factorial;
    while (factorial > 1) {
        factorial--;
        newFactorial *= factorial;
    }
    return newFactorial;
}

Answer 4

 function firstFactorial(num) { const output = eval(Array.from({length: num}, (_, index) => (index + 1)).reverse().join("*")); return output; } console.log(firstFactorial(8));

Rather than iterating through all the numbers using for loop or recursion . I used built-in Javascript functions. I first created an array of length 1-N using Array.from Then, I reversed that array and joined it with * . Then, I used the eval function to get evaluate the expression. You can also shrink it down to just one line. So the code will be: const findFactorial = num => eval(Array.from({length: num}, (_, index) => (index + 1)).reverse().join("*")