Set In JavaScript

What is a Set in JavaScript?

A Set is a built-in collection in JavaScript that allows you to store unique values of any type. A Set automatically removes duplicate values and stores them in an ordered fashion. It's similar to an array but with a few key differences.

Key Characteristics of a Set:

1. Unique Values: A Set can only contain unique values (no duplicates).

2. No Indexes: A Set does not use indexes to access elements. You can't access elements by index, unlike arrays.

3. Iterates in Insertion Order: The values in a Set are iterated in the order in which they were added.

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Creating a Set

You can create a Set using the Set constructor:

const mySet = new Set();

Alternatively, you can initialize a Set with an array or other iterable object:

const numbers = new Set([1, 2, 3, 4, 5]);

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Basic Operations on a Set

1. Add Method

You can add elements to a Set using the add() method. If you try to add a duplicate value, it will be ignored.

const mySet = new Set();

mySet.add(1);
mySet.add(2);
mySet.add(3);
mySet.add(2); // Duplicate value, will be ignored

console.log(mySet); // Output: Set { 1, 2, 3 }

2. Delete Method

The delete() method removes a specific element from the Set.

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

mySet.delete(2); // Removes 2 from the set

console.log(mySet); // Output: Set { 1, 3, 4 }

3. Has Method

The has() method checks if a particular element exists in the Set.

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

console.log(mySet.has(2)); // Output: true
console.log(mySet.has(4)); // Output: false

4. Size Property

The size property returns the number of unique elements in the Set.

const mySet = new Set([1, 2, 3, 4, 5]);

console.log(mySet.size); // Output: 5

5. Clear Method

The clear() method removes all elements from the Set.

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

mySet.clear();

console.log(mySet); // Output: Set {}

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Iterating Over a Set

You can iterate over a Set in several ways.

1. forEach Method

The forEach() method executes a provided function once for each element in the Set.

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

mySet.forEach((value) => {
  console.log(value);
});
// Output:
// 1
// 2
// 3

2. for...of Loop

You can use the for...of loop to iterate over the Set:

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

for (const value of mySet) {
  console.log(value);
}
// Output:
// 1
// 2
// 3

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Comparison: Set vs. Array

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Common Use Cases for Set

1. Removing Duplicates: You can use a Set to remove duplicate values from an array.

    const numbers = [1, 2, 2, 3, 4, 4, 5];
    const uniqueNumbers = [...new Set(numbers)];
    console.log(uniqueNumbers); // Output: [1, 2, 3, 4, 5]
   

2. Checking for Membership: A Set is very useful for checking if a value exists because of the fast lookup times.

    const uniqueSet = new Set([1, 2, 3, 4, 5]);
    console.log(uniqueSet.has(3)); // Output: true
    console.log(uniqueSet.has(6)); // Output: false
   

3. Storing Unique Values from Multiple Arrays:

    const array1 = [1, 2, 3];
    const array2 = [3, 4, 5];
    const combinedSet = new Set([...array1, ...array2]);
    console.log([...combinedSet]); // Output: [1, 2, 3, 4, 5]
   

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Summary of Key Methods

• add(value): Adds a value to the Set.

• delete(value): Deletes a specific value from the Set.

• has(value): Checks if a value exists in the Set.

• clear(): Removes all values from the Set.

• size: Returns the number of values in the Set.