Factorial function returning NAN

Question

I am new to javascript, I am trying to write a function that calculate the factorial of a given number and also replace the fourth element. I expect when the code above is run, it should produce 6GeXmanX but instead i am getting NaNXermXny

function Recursion(num) {
  
  if (num=== 0 || num===1){
    return 1;
  }
  result= Recursion(num-1)*num;
  
  results = result + 'Germany'
  const str = results.split('')
  const nth = 4
  var replaceWith = 'X'
  for (var i = nth-1; i < str.length-1; i+=nth){
    str[i]= replaceWith;
    
    
  }
  //y = (results.join(""))
  return (str.join(""));
  
  }
  


  // code goes here  
   
// keep this function call here 
console.log(Recursion(3));

Answer 1

First, you need to split the factorial function into a separate function.

Second, in the for condition, the i should be i < str.length not i < str.length - 1 as it will not iterate over the last letter.

function factorial(num) {
  
  if (num=== 0 || num===1){
    return 1;
  }
  return  factorial(num-1)*num;
  
}
  
  
function func(num) {
  let results = factorial(num) + 'Germany'
  const str = results.split('')
  const nth = 4
  var replaceWith = 'X'
  for (var i = nth-1; i < str.length; i+=nth){
    str[i]= replaceWith;
  }
  //y = (results.join(""))
  return (str.join(""));
  
  }
  


  // code goes here  
   
// keep this function call here 
console.log(func(3));