Tell about collections Map and Set in JavaScript — what do you know about them?

Map and Set are collections in JavaScript introduced in ES6 that extend data handling capabilities compared to regular objects and arrays.

Map is a collection of key-value pairs where keys can be of any type (objects, functions, primitives). Unlike regular objects, Map preserves the insertion order of elements and has convenient methods for working:

• set(key, value) — add or update an element
• get(key) — retrieve a value by key
• has(key) — check for the presence of a key
• delete(key) — remove an element
• size — number of elements

Example:

const map = new Map();
map.set('a', 1);
map.set({}, 2);
console.log(map.get('a')); // 1
console.log(map.size); // 2

Set is a collection of unique values of any type. It automatically excludes duplicates and maintains insertion order:

• add(value) — add an element
• has(value) — check for presence
• delete(value) — remove an element
• size — number of elements

Example:

const set = new Set();
set.add(1);
set.add(1);
set.add('text');
console.log(set.size); // 2

Both collections support iteration, which is convenient for traversing elements.