I am trying this simple code to calculate factorial of 5. But I am getting "undefined" as the result. I am aware of other methods but what is wrong with this?
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title> Learning </title>
<head>
<body>
<h2> Wele<h2>
<p id="demo"></p>
<script>
var fact=5;
function calfact(num)
{
if(num!=1)
{
fact=fact*(num-1);
num=num-1;
calfact(num);
}
else
{
return fact;
}
}
document.getElementById("demo").innerHTML=calfact(5);
</script>
</body>
</html>
I am trying this simple code to calculate factorial of 5. But I am getting "undefined" as the result. I am aware of other methods but what is wrong with this?
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title> Learning </title>
<head>
<body>
<h2> Wele<h2>
<p id="demo"></p>
<script>
var fact=5;
function calfact(num)
{
if(num!=1)
{
fact=fact*(num-1);
num=num-1;
calfact(num);
}
else
{
return fact;
}
}
document.getElementById("demo").innerHTML=calfact(5);
</script>
</body>
</html>
- 2 if (num!=1) the function returns nothing (undefined) – Jonas Wilms Commented Apr 15, 2017 at 13:43
- Possible duplicate of Fast factorial function in JavaScript – Krisztián Balla Commented Sep 15, 2018 at 13:02
3 Answers
Reset to default 3If you want a result from a recursive function, all code paths through the function must return something. Your code isn't returning anything in the num!=1 case. It should be returning the result of calling itself, e.g. (see the *** line):
var fact=5;
function calfact(num)
{
if(num!=1)
{
fact=fact*(num-1);
num=num-1;
return calfact(num); // ***
}
else
{
return fact;
}
}
Your function is using a global variable, which isn't a great idea as it means the funtion isn't self-contained; and isn't a true factorial function, because you're effectively using two inputs (fact — the global and num, the argument)
If you want a true factorial, you don't need a global variable, just work from the argument itself:
function factorial(num) {
if (num < 0) {
throw new Error("num must not be negative");
}
if (num <= 1) {
// Both 1! and 0! are defined as 1
return 1;
}
return num * factorial(num - 1);
}
console.log(factorial(5)); // 120Or of course, more pactly:
function factorial(num) {
if (num < 0) {
throw new Error("num must not be negative");
}
return num <= 1 ? 1 : num * factorial(num - 1);
}
(More about 0!: https://en.wikipedia/wiki/Factorial)
var fact=5;
function calfact(num){
if(num!=1){
fact=fact*(num-1);
num=num-1;
return calfact(num);//the missing thing
}else{
return fact;//why fact? i think it should be 1
}
}
By the way, your approach is maybe working, but really bad style.May do this:
function calfact(num){
if(num!=1){
return calfact(num-1)*num;
}else{
return 1;
}
}
Or short:
calfact=num=>num==1?1:calfact(num-1)*num;
You can use Tail Recursion, which is more efficient in case of memory.
const factorial = (n, acc = 1) => n == 0 || n == 1 ? acc : factorial(n - 1, acc * n);
console.log(factorial(10))