Sets represent a data structure that can only store unique values. In JavaScript, the set functionality defines a Set object.
const mySet = new Set();
Passing an array of values to the constructor:
const arr = [1, 1, 2, 3, 4, 5, 2, 4];
const numbers = new Set(arr);
console.log(numbers); // Set(5) {1, 2, 3, 4, 5}
A set can store only unique values, then when creating it, the repeated values that are in the array ,
are removed.
You can use the size method to check the number of elements.
const arr = [1, 1, 2, 3, 4, 5, 2, 4];
const numbers = new Set(arr);
console.log(numbers.size); //5
The add method is used to add data:
const mySet = new Set();
mySet.add(1);
mySet.add(3);
mySet.add(5);
Since the add method returns a reference to the same set, we can call methods in a chain:
mySet.add(1).add(3).add(5);
The delete method is used to remove elements:
let mySet = new Set();
mySet.add(1).add(3).add(5);
mySet.delete(3);
console.log(mySet); //Set(2) {1, 5}
The clear method removes all elements from the set:
let mySet = new Set();
mySet.add(1).add(3).add(5);
mySet.clear();
console.log(mySet);
If you need to check if an element is in a set, then the has() method is used. If the element exists, then the method returns true, otherwise it returns false:
let mySet = new Set();
mySet.add(1).add(3).add(5);
console.log(mySet.has(3)); // true
console.log(mySet.has(32)); // false
Iterating set
The forEach() method is used to iterate over the elements of a set:
const arr = [1, 2, 3, 5];
const mySet = new Set(arr);
numbers.forEach(function (value1, value2, set) {
console.log(value1);
})
//Console: 1
2
3
5
For a set directly, the first and second parameters represent the current element being iterated over; the third parameter is the iterable set.
Iterating with a for of loop
const mySet = new Set([1, 2, 3, 5]);
for (n of mySet ) {
console.log(n);
}
Getting an iterator
The Set object also has a number of methods that return an iterator, more specifically a SetIterator object. These are the methods : values() , keys(), entries():
const numbers = new Set([1, 2, 3, 5]);
console.log(numbers.values()); // SetIterator {1, 2, 3, 5}
console.log(numbers.keys()); // SetIterator {1, 2, 3, 5}
console.log(numbers.entries()); // SetIterator {1 => 1, 2 => 2, 3 => 3, 5 => 5}
The returned iterator we can use to get set objects:
const people = new Set(["Tom", "Bob", "Sam"]);
const iterator = people.values();
console.log(iterator.next()); // {value: "Tom", done: false}
console.log(iterator.next()); // {value: "Bob", done: false}
console.log(iterator.next()); // {value: "Sam", done: false}
console.log(iterator.next()); // {value: undefined, done: true}
Remove duplicate elements
const peopleArray = ["Tom", "Bob", "Sam", "Alice", "Sam", "Kate", "Tom"];
const peopleSet = new Set(peopleArray);
const newPeopleArray = Array.from(peopleSet);
console.log(newPeopleArray); // ["Tom", "Bob", "Sam", "Alice", "Kate"]
Here, to create a new array with non-repeating elements, the Array.from() function is used, which, as
argument receives a Set object.