ES6: All about Sets

The Set object lets you store unique values of any type, whether primitive values(strings, numbers or booleans) or object references.

Creating a set:

There are 2 ways to create a set, which are –

1. An Empty Set

An empty set does not has any value and after creation we need to add values using add() method.

const mySet = new Set()

2. A set with some values

If we want to initialize a set with some pre-defined value and then just pass an iterable to it as shown below –

const mySet = new Set([1,2,3,4,5,6,7,8,9]);

Adding an element to a Set:

We can add elements to a set using add() method provided by the Set class.

You can see above that we tried to add 5 twice but set just added it once, as said in the definition above, set stores unique elements only.

Deleting element from a Set:

1. Deleting a single element from the Set

To delete any specific element from a set, just call delete() and pass the element to be deleted as param.

2. Deleting all elements from the Set

To delete all the elements of a set we can just use the clear() method

Finding size of a Set:

To find the size of a set we can use size property of Set class.


Check existence of a element in Set:

To check whether an element exists in the Set, we use has() method of Set class.

mySet.has(1) //true
mySet.has(25) //false

Iterating a Set:

There are many ways to iterate over the elements of a set –

  • using for of loop
  • using forEach loop
  • using array conversion
  • using keys() methods
  • using values() method
  • using entries() method

In Set you observe that key and value of each element is same hence keys() and values() gives you same array of elements for a Set.

Mergin multiple Set:

To merge two or more sets we can use spread operator as shown below.

var merged = new Set([...set1, ...set2, ...set3])

Converting Set to Array:

1. Using Array.from() method

let myArr = Array.from(mySet);

2. Using spread operator

let myArr = [...mySet];

Operations of Set

1. Subset

File:Example of A is a proper subset of B.svg

a set A is a subset of a set B, or equivalently B is a superset of A, if A is “contained” inside B, that is, all elements of A are also elements of B.

2. Union

The union of two sets A and B is the set of elements which are in A, in B, or in both A and B

3. Intersection

the intersection of two sets A and B is the set that contains all elements of A that also belong to B (or equivalently, all elements of B that also belong to A), but no other elements.

4. Difference

The difference of set A from setB, denoted by B-A, is the set of all the elements of set B that are not in set A.

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