Cut first char from string.

Compare the new ES6 spread operator with the traditional concat() method and push

performance comparison of ways to find if an array contains a value

comparing Object.hasOwn(obj, "foo") with "foo" in obj

comparing Object.hasOwn(obj, "foo") with "foo" in obj

Various ways of getting A  Δ B = (A\B) ∪ (B\A) = (A ∪ B) \ (A ∩ B)