[JavaScript] Set Object

The Set object lets you store unique values of any type, whether primitive values or object references.

Create an Set Object

The Set constructor creates a Set object.

const set = new Set(); // Set(0) {}
const set = new Set([1, 2, 3, 3]); // Set(3) {1, 2, 3}
const set = new Set('Hello'); // Set(4) {'H', 'e', 'l', 'o'}

Set objects consider that all NaNs are the same.

console.log(NaN === NaN); // false
console.log(+0 === -0); // true

const set = new Set([NaN, NaN]); // Set(1) {NaN}
const set = new Set([+0, -0]); // Set(1) {0}

Set Instance

size

This property returns the number of values in the Set object.

It only has a getter.

const { size } = new Set([1, 2, 3, 3]); // 3

Set Method

add()

This method adds value to the Set object and returns the Set object with added value.

const set = new Set();

set.add(1).add(2); // Set(2) {1, 2}

clear()

This method removes all elements from the Set object.

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

set.clear(); // Set(0) {}

delete(value)

This method removes the element associated with the value and returns a boolean asserting whether an element was successfully removed or not.

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

set.delete(0); // false
set.delete(2); // true
// Set(2) {1, 3}

has(value)

This method returns a boolean asserting whether an element is present with the given value in the Set object or not.

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

set.has(2); // true
set.has(4); // false

values() and keys()

The values() method returns a new iterator object that yields the values for each element in the Set object in insertion order.

The keys() method is an alias for values() method.

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

set.values(); // SetIterator
set.keys(); // SetIterator

entries()

This method returns a new iterator object that contains an array of [value, value] for each element in the Set object, in insertion order.

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

set.entries(); // SetIterator

forEach()

This method calls the callback function once for each value present in the Set object, in insertion order.

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

set.forEach((e) => console.log(e));

We can traverse the Set object in other ways.

// for ... of
for (const e of set) {
  console.log(e);
}

// Spread Operator
console.log([...set]);

Mathematical Set Operation

Intersection

Set.prototype.intersection = function (set) {
  return new Set([...this].filter(e => set.has(e)));
};

Union

Set.prototype.union = function (set) {
  return new Set([...this, ...set]);
};

Difference

Set.prototype.difference = function (set) {
  return new Set([...this].filter(e => !set.has(e)));
};

Is Superset

Set.prototype.isSuperset = function (subset) {
  const supersetArr = [...this];
  return [...subset].every(e => supersetArr.includes(e));
};