Basically I'm talking about expansions done in javascript.
Some examples are:
1) Array.prototype.join()
Example:
const elements = ['Fire', 'Air', 'Water'];
console.log(elements.join());
// expected output: "Fire,Air,Water"
2) Spread operator (...)
Example:
const arr1 = [1, 2, 3];
const arr2 = [4, 5, 6];
const arr3 = [7, 8, 9];
const arrWrap = [...arr1, ...arr2, ...arr3];
3) IndexOf or Set.prototype.has().
I think if expanding set operation is not easy, then it may be added to array. Like TArray.has().
BTW, can I write some of these functions using type helpers in Free Pascal?