Javascript function to compute factorial of integer number

Question

I am want to have function to computer factorial of integer numbers. I created function with loop under it and then call the function to pass the number and get the result. But it outcomes undefined, although all variables are declared properly.

<script>
   var userInput;
   var num;
   var i =1;
   var fact;
               
   function myFactor (num){
     
   fact = num * i;
   
    for (i; i <= num; i++) {
    fact = fact * i;
    
    return fact;
    }
   }
   
   
   var result = myFactor(fact);
   userInput = prompt("Enter Value:",""); 
   num = parseInt (userInput);   
   
   document.write(result);
</script>

There are many codes that achieve this but I want to learn that why my code does not work.

If you read your code from top>to>bottom (like a JS parser would) you'll easily notice all your errors, undefineds, unsets, too early calls wrong arguments etc you're doing. — Roko C. Buljan, Oct 23 '15 at 00:45
@guest271314 I added 'var fact = 1;' before that but still have same result. nothing changed. — Maihan Nijat, Oct 23 '15 at 00:46
Your function calculates the factorial, not the factors of a number. Factors are the numbers that you can multiply together to get the input number. For instance, the factors of 10 are 2 and 5. — Barmar, Oct 23 '15 at 01:01
Possible duplicate of [Fast factorial function in JavaScript](https://stackoverflow.com/questions/3959211/fast-factorial-function-in-javascript) — Krisztián Balla, Sep 15 '18 at 13:02

score 1 · Accepted Answer · answered Oct 23 '15 at 01:02

1

You forgot the closing brackets before and after returning and to call the function with the number given by the user and one iteration too many.

var userInput;
var num;
var i =1;
var fact;

function myFactor (num){    
  fact = num * i;
  for (i; i < num; i++) {
    fact = fact * i;
  }
  return fact
}

var result;
userInput = prompt("Enter Value:","");  
num = parseInt (userInput);         
result = myFactor(num);
document.write(result);

Should work now. BTW: the function computes a factorial, factoring is something different. Ow, too late again.

answered Oct 23 '15 at 01:02

deamentiaemundi

5,502
2
12
20

It works. Just add ; for closing the return statement. – Maihan Nijat Oct 23 '15 at 01:07
1

@deamentiaemundi This is correct, but this function (as well as OP's) is not idempotent. You are modifying the global `i` from within the `myFactor` function, so calling `myFactor` multiple times in a row will produce incorrect results on subsequent calls. For clarity and correctness, I would declare and initialize both `i` and `fact` inside `myFactor`. – Igor Raush Oct 23 '15 at 01:09
You don't need to in ECMA-script. But you're right, of course, some see it as a better style to do so and it is sometimes difficult to tell where it is possible to drop and where not.. – deamentiaemundi Oct 23 '15 at 01:09
@IgorRaush I'm too slow for this world ;-) But I like to change only so much as needed in the OPs code not more. I think it is easier for them to tell which parts were broken. – deamentiaemundi Oct 23 '15 at 01:11

score 0 · Answer 2 · edited Oct 23 '15 at 00:59

0

try:

var userInput;
var num;

var fact;

function myFactor(num) {

    var i = 1;
    fact = num * i;

    for (i; i <= num; i++) {
        fact = fact * i;

        return fact;
    }
}
userInput = prompt("Enter Value:", "");
num = parseInt(userInput);
var result = myFactor(num);

alert(result);

edited Oct 23 '15 at 00:59

Barmar

741,623
53
500
612

answered Oct 23 '15 at 00:49

Kevin Simple

1,225
10
22

It doesn't return the factoring result. It returns back the same number entered. – Maihan Nijat Oct 23 '15 at 00:51
give me sample input and output – Kevin Simple Oct 23 '15 at 00:56
Factor of 5 equals to 120. It is like 5*4*3*2*1=20 – Maihan Nijat Oct 23 '15 at 00:58

Javascript function to compute factorial of integer number

2 Answers2