JavaScript Sets

A JavaScript Set is a collection of unique values.

Each value can only occur once in a Set.

Essential Set Methods

Method Description
new Set() Creates a new Set
add() Adds a new element to the Set
delete() Removes an element from a Set
has() Returns true if a value exists in the Set
forEach() Invokes a callback for each element in the Set
values() Returns an iterator with all the values in a Set
Property Description
size Returns the number of elements in a Set

How to Create a Set

You can create a JavaScript Set by:

Passing an Array to new Set()

Create a new Set and use add() to add values

Create a new Set and use add() to add variables

The new Set() Method

Pass an Array to the new Set() constructor:


// Create a Set
const letters = new Set(["a","b","c"]);

Create a Set and add values:

// Create a Set
const letters = new Set();

// Add Values to the Set


Create a Set and add variables:


The add() Method

If you add equal elements, only the first will be saved:


The forEach() Method

The forEach() method invokes (calls) a function for each Set element:


The values() Method

The values() method returns a new iterator object containing all the values in a Set:


letters.values()   // Returns [object Set Iterator]

Now you can use the Iterator object to access the elements: