Answers for "what does the ! in javascript"

?. in javascript

The optional chaining operator (?.) enables you to read the value of a
property located deep within a chain of connected objects without having
to check that each reference in the chain is valid.

what is ... in javascript

function sum(...numbers) {
	return numbers.reduce((accumulator, current) => {
		return accumulator += current;
	});
};
 
sum(1,2) // 3
sum(1,2,3,4,5) // 15