Diff Two Arrays Exclamation Mark

Tell us what’s happening:
Hello, in the solution of the problem appears an exclamation mark before the array.
What’s is the meaning of this? I understand the logic without the exclamation mark, i’m very confused.

Thank you.

Your code so far


function diffArray(arr1, arr2) {
  return arr1
    .concat(arr2)
    .filter(
      (element) => !arr1.includes(element) || !arr2.includes(element)
    );
  // Same, same; but different.
  return newArr;
}

diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]);

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Link to the challenge:

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Thank you.

The exclamation mark is a NOT operator, it flips the Boolean value of whatever it is put in front of

So if includes return false, it becomes true and viceversa