First Factorial

gistfile1.txt

function FirstFactorial(num) { 

  // code goes here  
  //when num is finally equal to 1 or 0, the function will terminate
  if (num === 0 || num === 1){
      return 1;
  }
  /*Multiplies the value of num by it's own value -1 each time this function loops. 
  The function will call itself over and over again until num is equal to 1.*/ 
  return num * FirstFactorial(num-1); 
        
}
   
// keep this function call here 
FirstFactorial(readline());  

This looks good. Recursion is a good choice for this problem.