Modern JavaScript provides powerful data structures called Map and Set. These were introduced in ES6 to solve some limitations of traditional Objects and Arrays. If you learning modern JavaScript, React, Node.js then understanding Map and Set is very important.

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What Map in JavaScript

A Map is a special data structure used to store KEY-VALUE pairs which is very similar to objects. For example :

const user = new Map();

user.set("name", "Rahul");
user.set("age", 21);

console.log(user);

Understanding the Structure

Key   ->    Value

"name"  -> "Rahul"
"age"    -> 21

This is how Map stores data.

Creating a Map and Adding Values to Map

const map = new Map();

This is the way you can create a new Map .

map.set("city", "Delhi");

This is the way you can set values to a Map.

Getting Values From Map

console.log(map.get("city"));

get() methods gives the values from the Map. This way you can get values from map.

Removing Values

map.delete("city");

Like in object delete is used to remove values , here also delete is used to remove values from Map.

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What Set is

A Set is a special data structure used to store Unique values only. Duplicate values are automatically removed. For example :

const numbers = new Set();

numbers.add(1);
numbers.add(2);
numbers.add(2);

console.log(numbers);

Output :

Set(2) {1, 2}

Here, 2 appears only once because Sets do not allow duplicates.

Creating a Set and Adding Values

We can create a set by :

const set = new Set();

After creating a Set , we can add values using .add() methods

set.add("JavaScript");

Checking Values

checking values has to done using has() methods in set.

console.log(set.has("JavaScript"));

Removing Values

To remove values from set delete() is used to remove values from set.

set.delete("JavaScript");

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Difference between Map and Object

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Difference between Set and Array

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When to use Map and Set

Use Map when :

• key-value stored is needed

• keys are dynamic

• non-string keys are required

• frequent additions/ removals happen

Use set when :

• unique values are required

• duplicate removal is needed

• fast existence checking is needed

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Wrapping Up 🚀

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