A Set in JavaScript is used to store a unique collection of items, meaning no duplicates are allowed.

Sets internally use a hash table which makes search, insert, and delete operations faster than arrays. Please note that a hash table data structure allows these operations to be performed on average in constant time.

• Set maintains insertion order. When we access items, we get them in the same order as inserted.
• Only Unique Keys are allowed. If we insert the same key with a different value, it overwrites the previous one.
• A Set can be created either empty or by providing an iterable like an array or string.

Example Usage

// using an array
let s1 = new Set([10, 30, 30, 40, 40]);
console.log(s1);
let s2 = new Set(["gfg", "gfg", "geeks"]);
console.log(s2);
 
// using string
let s3 = new Set("fooooooood");
console.log(s3);
 
// an empty set
let s4 = new Set();
console.log(s4);

Output

Set(3) { 10, 30, 40 }
Set(2) { 'C75', 'Coding75' }
Set(3) { 'f', 'o', 'd' }
Set(0) {}

Key Characteristics of Sets:

• Unique Values: A Set cannot contain duplicate values.
• Ordered: Sets maintain the insertion order of elements.
• Iterable: Sets can be iterated using loops or methods like forEach.
• No Indexing: Unlike arrays, Sets do not support indexing.

Methods of Set in JavaScript

• Set.add(value): Adds the new element with a specified value at the end of the Set object.
• Set.delete(value): Deletes an element with the specified value from the Set object.
• Set.clear(): Removes all the elements from the Set.
• Set.entries(): Returns an iterator object which contains an array having the entries of the Set, in the insertion order.
• Set.has(value): Returns true if the specified value is present in the Set object.
• Set.values(): Returns all the values from the Set in the same insertion order.
• Set.keys(): Also returns all the values from the Set in the insertion order.
• Set.forEach(callback): Executes the given function once for every element in the Set, in the insertion order.
• Set.prototype[@@iterator]() : Returns a Set iterator function, which is values() function by default.

DSA Problems On Set In JavaScript

• Union of Two Arrays
• Intersection of Two Arrays
• Distinct Elements in an Array
• Check for Disjoint Arrays or Sets
• Check if an Array is a Subset of Another
• Duplicate within K Distance in an Array
• 2 Sum – Check for Pair with Target Sum
• Only Repeating Element From 1 To n-1
• Longest Consecutive Sequence
• Smallest Subarray with k Distinct Numbers