# Everything You Need to Know About JavaScript Set

20 January, 2023

4

4

1

Contributors

JavaScript `objects`

and `arrays`

are the most used data structures act as collections of data. Until `ES6`

there were limited options with developers. But with ES6 we have got two new flexible and easy to use data structures, `Map`

and `Set`

.

In this article, we will learn about `Set`

and we are going to make some salad(🥗) too!

## Set

A `Set`

is a collection of `unique`

(distinct) elements where each of the elements can be of any type. The `Set`

is also an ordered collection of elements. It means the retrieval order of the elements will be the same as that of the insertion order.

The JavaScript Set behaves the same way as the mathematical set.

Create a `Set`

,

`const set = new Set();`

console.log(set);

Output,

`Set(0) {}`

Initialize a `Set`

and create,

`const fruteSet = new Set(['🍉', '🍎', '🍈', '🍏']);`

console.log(fruteSet);

Output,

`Set(4) {"🍉", "🍎", "🍈", "🍏"}`

## Set methods - Let's make some Salad 🥗!

`Set`

has methods to add an element to it, delete elements from it, check if an element exists in it, and to clear it completely. Let us see it by making some salad!

### Add vegetables

Use the `add(element)`

method to add an element to the `Set`

.

const saladSet = new Set();

saladSet.add('🍅');

saladSet.add('🥑');

saladSet.add('🥕');

saladSet.add('🥒');

console.log(saladSet);

Alright, we have added the vegetables. The output so far,

`Set(4) {"🍅", "🥑", "🥕", "🥒"}`

### Add another Cucumber - Can we?

I love cucumber! How about adding one more of it. Can I? Oh no, I can't. The `Set`

is a collection of `unique`

elements.

`saladSet.add('🥒');`

console.log(saladSet);

Output is still as before, nothing got added to the `saladSet`

.

`Set(4) {"🍅", "🥑", "🥕", "🥒"}`

### Does it have a Carrot(🥕) or a Broccoli(🥦)?

Use the `has(element)`

method to search an element in a `Set`

.

console.log('Does the Salad has Carrot?', saladSet.has('🥕')); console.log('Does the Salad has Broccoli?', saladSet.has('🥦'));

Use the `delete(element)`

method to remove an element from a `Set`

.

`saladSet.delete('🥑');`

console.log('I do not like 🥑, remove from the salad:', saladSet);

Now our salad set is,

`I do not like 🥑, remove from the salad: Set(3) {"🍅", "🥕", "🥒"}`

### Let's clean up, finish the salad!

Use the `clear()`

method to remove all the elements from a `Set`

.

`saladSet.clear();`

console.log('Finished it:', saladSet);

Output,

`Finished it: Set(0) {}`

## Iteration with Set

The `Set`

has a method called, `values()`

which returns a `SetIterator`

to get all the values.

const houseNos = new Set([360, 567, 101]); console.log(houseNos.values());

Output,

`SetIterator {360, 567, 101}`

We can use `forEach`

or `for-of`

loop on this to retrieve the values.

Interesting fact: JavaScript emphasizes to make

`Set`

compatible with`Map`

. That's why we find two`Set`

methods,`keys()`

and`entries()`

like Map.

As `Set`

doesn't have a key, the `keys()`

method returns a SetIterator to retrieve values.

`console.log(houseNos.keys());`

Output,

`SetIterator {360, 567, 101}`

Try `entries()`

now. For `Map`

it returns the iterator to retrieve key-value pairs. There is no key for the Set. Hence the `entries()`

method returns a SetIterator to retrieve the value-value pairs.

`console.log(houseNos.entries());`

Output,

`SetIterator {360 => 360, 567 => 567, 101 => 101}`

### Let's Enumerate

We can enumerate over a Set using `forEach`

and `for-of`

loop.

`houseNos.forEach((value) => { `

console.log(value);

});

Output,

`360`

567

101

With `for-of`

,

`for(const value of houseNos) { `

console.log(value);

}

## Set and object

A `Set`

can have elements of any type, even objects.

const person = { 'name': 'Alex', 'age': 32 }; const pSet = new Set();

pSet.add(person);

console.log(pSet);

Output,

No surprise. The Set contains one element that is an object. Let us now, change a property of the object and add it to the set again.

person.name = 'Bob'; pSet.add(person);

console.log(pSet);

What do you think about the output? Two `person`

objects or the one? Here is the output,

`Set`

is the collection of unique elements. By changing the property of the object, we haven't changed the object itself. Hence `Set`

will not allow duplicate elements.

## Set and Array

An array, like a Set, allows adding and removing elements to it. But Set is different than array and it is not meant to replace array. Using `Set`

as an add-on to array actually give more muscles.

The major difference between an array and Set is, array allows duplicate elements where Set is for distinct elements. Some of the Set operations(delete) are also faster than array operations(shift, splice).

The

`Set`

data structure is not a replacement of the`array`

.`Set`

along with array can solve interesting problems.

## Convert Set to an array

In many situations, you may want to convert a Set to an array. In fact, it is very easy!

`const arr = [...houseNos];`

console.log(arr);

Output,

## Unique values from an array using Set

The most common usage of the Set data structure is to get unique values from an array.

const mixedFruit = ['🍉', '🍎', '🍉', '🍈', '🍏', '🍎', '🍈',];

const mixedFruitSet = new Set(mixedFruit); console.log(mixedFruitSet);

Output,

`Set(4) {"🍉", "🍎", "🍈", "🍏"}`

## Set Operations

It is very easy to perform the basic set operations like, `union`

, `intersection`

, `diference`

, `superset`

, `subset`

etc with `Set`

and array together. Let us take these two sets to perform these oprtations,

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

const second = new Set([3, 4, 5]);

## Union

`Union`

of the sets A and B, denoted A ∪ B, is the set of all items that is a member of A, or B, or both. For example. the union of {1, 2, 3} and {3, 4, 5} is the set {1, 2, 3, 4, 5}.

const union = new Set([...first, ...second]);

console.log('Union:', union);

Output,

`Union: Set(5) {1, 2, 3, 4, 5}`

## Intersection

`Intersection`

of the sets A and B, denoted A ∩ B, is the set of all objects that are members of both A and B. For example, the intersection of {1, 2, 3} and {3, 4, 5} is the set {3}.

const intersection = new Set([...first].filter(elem => second.has(elem)));

console.log('Intersection:', intersection);

Output,

`Intersection: Set(1) {3}`

## Difference

`Set difference`

of U and A, denoted U \ A, is the set of all members of U that are not members of A. The set difference {1, 2, 3} \ {3, 4, 5} is {1, 2}, while conversely, the set difference {3, 4, 5} \ {1, 2, 3} is {4, 5}.

const difference = new Set([...first].filter(elem => !second.has(elem)));

Output,

`Difference: Set(2) {1, 2}`

## Superset

A set A is a subset of a set B if all elements of A are also elements of B; B is then a superset of A.

const isSuperset = (set, subset) => {

for (let elem of subset) {

if (!set.has(elem)) {

return false;

}

}

return true;

}

console.log('Is Superset?', isSuperset(first, second));

Output,

`Is Superset? false`

Here is some more information about `Set`

vs `Array`

: