Is finding the factorial of 5000 possible in javascript

Question

I want to find the factorial of 5000 but once I try to pass 100 it'll return infinity. Is there are way to bypass this and get the result? I am trying to get the time it takes to solve this.

function testSpeed(n) {
    if (n > 0 && n <= 1) {
         return 1;
    } else {
         return n * testSpeed(n-1);
    }
}
console.log(testSpeed(5000));

Answer 1

As you've noticed, Javascript numbers can only get so big before they just become "Infinity". If you want to support bigger numbers, you'll have to use BigInt.

Examples:

// Without BigInt
console.log(100 ** 1000) // Infinity

// With BigInt
// (stackOverflow doesn't seem to print the result,
// unless I turn it into a string first)
console.log(String(100n ** 1000n)) // A really big number

So, for your specific bit of code, all you need to do is turn your numeric literals into BigInt literals, like this:

function testSpeed(n) {
  if (n > 0n && n <= 1n) {
      return 1n;
  } else {
      return n * testSpeed(n-1n);
  }
}

console.log(String(testSpeed(5000n)));

You'll find that youe computer can run that piece of code in a snap.