I have a pretty hard time understanding what is going on in this FreeCodeCamp exercise code:

function sumPrimes(num) {
  let primeNumbers = new Array;

  for (let i = 2; i <= num; i++) {
    if (primeNumbers.every(prime => i % prime !== 0)) {
      primeNumbers.push(i);
    }
  }
  return primeNumbers.reduce((sum, prime) => sum + prime);
}

console.log(sumPrimes(10));

Why does the every method here even work when the array (primeNumbers) is empty. And secondly how does the condition work with a parameter prime when there is nothing in the array from where does the function get the value for the parameter prime from?