Prime Numbers

A number is prime if it can be divided ONLY by 1 and by itself.

Let's create a function that checks if a number is prime:

function isPrime(number){
  let isPrime = true;
  for (let i = 2; i <= number / 2; i++) {
    if (number % i === 0) {
      isPrime = false;
      break;
    }
  }
  return isPrime;
}

If we find at least one number between 2 and it's half, then the number is not prime. So, isPrime gets false and that's it – we don't continue. Game over with that fella 😂

Let's call the function with a prime number and see what we get:

var number = 53;
var result = isPrime(number);
console.log(result); // true

We can also create an array to test multiple numbers with a foreach loop:

var numbers = [32, 2, 43, 423, 0, 2];

numbers.forEach(number => {
  var result = isPrime(number);
  console.log(number + " is prime: " + result);
});

This is a simple approach that works 😄

But if you want to get crazy about it (being more efficient, faster etc.), you can 😅

This is the new function:

function isPrime(number) {
var firstPrimes = [0, 1, 2, 3];
if (firstPrimes.includes(number)) {
  return true;
}

if (number % 2 === 0 || number % 3 === 0) {
  return false;
}

let isPrime = true;
for (let i = 5; i <= number / 2; i += 2) {
  if (number % i === 0) {
    isPrime = false;
    break;
  }
}

return isPrime;
}

😱

# Prime Numbers

Prime Numbers