JavaScript Rest Parameters - Exercise 1

It collects remaining function arguments into an array.

function logAll(...values) {
  console.log(values);
}

It must be the final parameter.

function join(separator, ...parts) {
  return parts.join(separator);
}

Yes. The collected values are available as a real array.

function count(...items) {
  return items.length;
}

They provide named array access to all remaining arguments.

function sum(...numbers) {
  return numbers.reduce((total, value) => total + value, 0);
}

No. A parameter list can contain only one rest parameter, and it must be last.

function collect(first, ...rest) {
  return [first, rest];
}

It gathers the remaining array elements into a new array.

const [first, ...others] = ['a', 'b', 'c'];

It gathers remaining properties into a new object.

const { id, ...details } = user;

Rest collects multiple values; spread expands an iterable or object.

const values = [1, 2];
const copy = [...values];
const [first, ...rest] = copy;

Yes. It becomes an empty array when no remaining arguments are supplied.

function count(...items) {
  return items.length;
}
count();

They let a function accept a flexible number of arguments while keeping them easy to process.

function firstAndLast(first, ...middle) {
  return { first, middle };
}