What are Map and Set objects?

Map is a collection of keyed values. Set is a collection of unique values.

Iteration over Map and Set is always in the insertion order, so we can’t say that these collections are unordered, but we can’t reorder elements or directly get an element by its number.

const map = new Map([['key', 1], ['key2', 'value']]);
const set = new Set([1, 2, 2, 3]);