What are Map and Set, how do they differ, and what are their features?

Map and Set are collections in JavaScript designed for storing data, but with different purposes:

• Map is a collection of key-value pairs. Keys can be of any type (objects, functions, primitives). Map maintains the order of insertion.

• Set is a collection of unique values. It cannot contain duplicates, and it also maintains the order of insertion.

Differences and features:

• Map stores key-value pairs, Set stores only values.
• In Map, you can quickly get a value by key; in Set, you check for the presence of a value.
• Map has methods set(key, value), get(key), has(key), delete(key), size.
• Set has methods add(value), has(value), delete(value), size.

Example:

const map = new Map();
map.set('a', 1);
map.set({}, 2);

const set = new Set();
set.add(1);
set.add(2);
set.add(1); // will not be added again, as it's a duplicate

console.log(map.get('a')); // 1
console.log(set.has(2)); // true