A JavaScript Set is a collection of unique values.

Each value can only occur once in a Set.

A Set can hold any value of any data type.

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
clear()	Removes all elements from a Set
forEach()	Invokes a callback for each element
values()	Returns an Iterator with all the values in a Set
keys()	Same as values()
entries()	Returns an Iterator with the [value,value] pairs from a Set

 

Property	Description
size	Returns the number 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:

Example

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

-

Create a Set and add literal values:

Example

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

// Add Values to the Set
letters.add("a");
letters.add("b");
letters.add("c");

-

Create a Set and add variables:

Example

// Create Variables
const a = "a";
const b = "b";
const c = "c";

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

// Add Variables to the Set
letters.add(a);
letters.add(b);
letters.add(c);

-

The add() Method

Example

letters.add("d");
letters.add("e");

-

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

Example

letters.add("a");
letters.add("b");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");

-

The forEach() Method

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

Example

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

// List all entries
let text = "";
letters.forEach (function(value) {
  text += value;
})

-

The values() Method

The values() method returns an Iterator object containing all the values in a Set:

Example

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

-

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

Example

// Create an Iterator
const myIterator = letters.values();

// List all Values
let text = "";
for (const entry of myIterator) {
  text += entry;
}

-

The keys() Method

A Set has no keys.

keys() returns the same as values().

This makes Sets compatible with Maps.

Example

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

-

The entries() Method

A Set has no keys.

entries() returns [value,value] pairs instead of [key,value] pairs.

This makes Sets compatible with Maps:

Example