The JavaScript Set object stores unique values of any type and automatically removes duplicates. 1. It ensures uniqueness — adding a duplicate value has no effect. 2. It can store any value including primitives and object references. 3. It maintains insertion order when iterating. 4. It is not index-based, so items cannot be accessed by index. 5. Common methods include add(), delete(), has(), clear(), and the size property. 6. Sets are iterable, allowing use of for...of, forEach, or the spread operator to convert to an array. 7. A common use case is removing duplicates from an array using [...new Set(array)]. 8. Sets are ideal for tracking unique items like IDs or tags and provide faster membership checks than arrays. The Set is a built-in, efficient JavaScript object for managing collections of distinct values.
The JavaScript Set object is a built-in data structure that allows you to store unique values of any type — whether primitive values like strings, numbers, or references to objects.
Unlike arrays, a Set automatically ensures that each value appears only once. This makes it super useful when you need to eliminate duplicates or work with a collection of distinct items.
Key Features of Set
- Stores unique values only — If you try to add a value that already exists, it will be ignored.
- Can hold any type of value — numbers, strings, booleans, objects, functions, etc.
- Maintains insertion order — values are iterated in the order they were added.
-
Not index-based — unlike arrays, you can’t access items by index (e.g.,
set[0]won’t work).
Basic Syntax
const mySet = new Set();
You can also initialize it with an iterable (like an array):
const mySet = new Set([1, 2, 2, 3, 4, 4]);
console.log(mySet); // Set { 1, 2, 3, 4 }Notice how duplicates are automatically removed.
Common Set Methods
Here are the most useful methods when working with Sets:
add(value)— adds a value to the setdelete(value)— removes a valuehas(value)— checks if a value exists (returnstrue/false)clear()— removes all valuessize— property that returns the number of elements
Example Usage
const colors = new Set();
colors.add('red');
colors.add('blue');
colors.add('red'); // duplicate, ignored
console.log(colors.has('red')); // true
console.log(colors.size); // 2
colors.delete('blue');
console.log(colors); // Set { 'red' }Iterating Over a Set
Since Sets are iterable, you can use for...of, forEach, or spread them into an array:
const items = new Set(['a', 'b', 'c']);
for (const item of items) {
console.log(item);
}
// Or convert to array
const arr = [...items];You can also use the spread operator to remove duplicates from an array quickly:
const uniqueArray = [...new Set([1, 2, 2, 3, 3, 4])]; // [1, 2, 3, 4]
When to Use Set
- Removing duplicates from a list
- Checking membership quickly (faster than arrays for
has()checks) - Tracking unique items like user IDs, event listeners, or tags
Basically, if you need a list where every item must be unique and you care about fast lookups, Set is a great choice.
It’s not complex — just a clean, efficient tool for handling uniqueness in JavaScript.
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