JavaScript

A Set is a built-in JavaScript object that lets you store unique values — no duplicates allowed!

Sets are useful when you need a collection of values where order doesn’t matter and no repetitions are allowed.

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✅ Key Features of Sets

• No duplicate values
• Insertion order is preserved
• Values can be of any type: string, number, object, etc.

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🧱 Creating a Set

You create a Set using the Set constructor:

const letters = new Set();

You can also pass an array to initialize it with values:

const numbers = new Set([1, 2, 3, 4]);

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➕ Adding Values

Use .add() to add items to a Set:

const fruits = new Set();

fruits.add("apple");
fruits.add("banana");
fruits.add("apple"); // duplicate, won't be added

console.log(fruits);

Output:

Set(2) { "apple", "banana" }

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➖ Removing Values

✅ delete()

fruits.delete("banana");

✅ clear()

fruits.clear(); // removes all values

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❓ Checking Values

✅ has()

console.log(fruits.has("apple")); // true
console.log(fruits.has("mango")); // false

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🔁 Looping Through a Set

Use for...of or forEach():

for (let fruit of fruits) {
  console.log(fruit);
}

OR

fruits.forEach(fruit => {
  console.log(fruit);
});

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🧮 Set Size

Use .size to get the number of elements:

console.log(fruits.size); // 2

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🧪 Example: Remove Duplicates from Array

const arr = [1, 2, 3, 2, 1, 4];
const unique = [...new Set(arr)];

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

🔹 Very handy for filtering out repeated values!

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🧾 Summary

Method	Description
add(value)	Adds a value
delete(value)	Removes a specific value
has(value)	Checks if value exists
clear()	Removes all values
size	Returns number of values

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🧠 When to Use a Set?

• Removing duplicates from arrays
• Storing a list of unique items (like tags, selected values, etc.)
• Fast lookup without caring about order

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