Map and Set in JavaScript

JavaScript offers Map and Set as modern data structures to solve common problems with traditional objects and arrays.

Let’s explore what they are, how they differ, and when to use them.

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🧠 What Is a Map?

A Map is a collection of key-value pairs, similar to an object, but with some improvements:

• Keys can be any type (objects, functions, primitives)
• Preserves insertion order
• Built-in methods to get, set, delete, and check entries

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✅ Map Example

```js id="map1"
const map = new Map();

map.set("name", "Rahul");
map.set("age", 22);
map.set(true, "Boolean key");

console.log(map.get("name")); // Rahul
console.log(map.has("age")); // true
console.log(map.size); // 3

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### 📊 Map Visual



```id="viz1"
Key → Value
"name"  → "Rahul"
"age"   → 22
true    → "Boolean key"

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⚡ Map vs Object

Feature	Map	Object
Key types	Any type	String / Symbol
Order preservation	Yes	Not guaranteed
Size property	map.size	Must compute manually
Iteration	Built-in	Manual / Object.keys

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🧠 What Is a Set?

A Set is a collection of unique values—duplicates are automatically removed.

• Can store any type of value
• Provides fast lookups and uniqueness checks

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✅ Set Example

```js id="set1"
const set = new Set([1, 2, 3, 2, 1]);

console.log(set); // Set(3) { 1, 2, 3 }
console.log(set.has(2)); // true

set.add(4);
console.log(set); // Set(4) { 1, 2, 3, 4 }

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### 📊 Set Visual



```id="viz2"
[1, 2, 3, 2, 1] → Set → {1, 2, 3}

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⚡ Set vs Array

Feature	Set	Array
Uniqueness	✅ Unique values	❌ Allows duplicates
Lookup speed	Fast	Linear search
Methods	add, delete, has	push, pop, includes

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🛠️ When to Use Map and Set

Use Map when:

• You need dynamic keys of any type
• You want ordered key-value storage
• You need built-in iteration over entries

Use Set when:

• You want unique values only
• You need to quickly check existence
• You want to remove duplicates from an array

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🔹 Removing Duplicates Example

```js id="set2"
const numbers = [1, 2, 3, 2, 4, 3];
const uniqueNumbers = [...new Set(numbers)];

console.log(uniqueNumbers); // [1, 2, 3, 4]

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### 🔹 Map for Counting Occurrences



```js id="map2"
const arr = ["apple", "banana", "apple"];
const countMap = new Map();

arr.forEach(item => {
  countMap.set(item, (countMap.get(item) || 0) + 1);
});

console.log(countMap);
// Map(2) { "apple" => 2, "banana" => 1 }

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⚡ Key Takeaways

• Map → flexible key-value storage, ordered, keys can be any type
• Set → collection of unique values, fast lookups, removes duplicates easily
• Solves common limitations of Objects and Arrays

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