# Set and Map — JavaScript

Source: https://www.geekswithgeeks.com/en/javascript/js-set-map

> Two built-in collections beyond arrays and objects.

## Set: unique values

A `Set` automatically drops duplicates and checks membership fast.

```js
const tags = new Set(["js", "web", "js"]);
console.log(tags);              // Set(2) {'js', 'web'}
console.log(tags.has("web"));   // true
tags.add("css");
```

## Map: any key type

Unlike a plain object, a `Map`'s keys can be any type, including numbers and objects.

```js
const scores = new Map();
scores.set("Ada", 92);
scores.set(1, "one");
console.log(scores.get("Ada"));  // 92
console.log(scores.size);        // 2
```

## Map vs plain object

Unlike objects, `Map` keys can be **any type**, insertion order is always preserved, and `.size` gives the count directly — better for dynamic key-value data.

## Iterating

Both are iterable directly with `for...of`: `for (const [key, val] of map)`.