Set

Sets are a new object type which allow to create collections of unique values. The values in a set can be either primitives like strings or integers and non-primitives like object literals or arrays.

const set = new Set([10, 10, 20, 30, 'Tom', {name: 'Mike'}]);
console.log(set);

Output:
Set(5) {10, 20, 30, "Tom", {name: 'Mike'}}

Set.prototype.add

Append new element with a specified value at the end of the Set object and return Set object

const set = new Set();
set.add(10);
set.add(10);
set.add(20);
set.add(30);
set.add('Tom');
set.add({name: 'Mike'});
console.log(set);

Output:
Set(5) {10, 20, 30, "Tom", {name: 'Mike'}}

Set.prototype.size

It returns the number of elements in the Set.

const set = new Set([10, 10, 20, 30, 30, 40, 'Tom', {name: 'Mike'}]);
console.log(set.size);  // Output: 6

Set.prototype.delete

It deletes an element with the specified value from the Set object

const set = new Set();
set.add(10).add(10).add(20).add(30).add(30).add(40).add('Tom').add({name: 'Mike'});
set.delete(20);
set.delete('Tom');
console.log(set);

Output:
Set(4) {10, 30, 40, {name: 'Mike'}}

Set.prototype.has

It returns true if the specified value is present in the Set object.

const set = new Set();
set.add(10).add(10).add(20).add(30).add(30).add(40).add('Tom').add({name: 'Mike'});
console.log(set.has('Tom'));    // Output: true
console.log(set.has('Mike'));   // Output: false

Set.prototype.clear

It removes all the element from the set.

const set = new Set();
set.add(10).add(10).add(20).add(30).add(30).add(40).add('Tom').add({name: 'Mike'});
set.clear();
console.log(set);   // Output: Set(0) {}

Iteration over Set

Set.prototype.forEach

It executes a provided function once for each value in the Set object, in insertion order

function logSetElements(value1, value2, set) {
  console.log(`s[${value1}] = ${value2}`);
}

new Set(['Mike', 'Tom', undefined]).forEach(logSetElements);

Output:
s[Mike] = Mike
s[Tom] = Tom
s[undefined] = undefined

Set.prototype.values

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

const names = new Set();
names.add('Tom');
names.add('Mike');

const setIterator = names.values();

console.log(setIterator);

Output:
SetIterator {"Tom", "Mike"}

Set.prototype.entries

The entries() method returns a new Iterator object that contains an array of [value, value] for each element in the Set object, in insertion order.
For Set objects there is no key like in Map objects. However, to keep the API similar to the Map object, each entry has the same value for its key and value here, so that an array [value, value] is returned.

const names = new Set();
names.add('Tom');
names.add('Mike');

const setIterator = names.entries();

for (const entry of setIterator) {
  console.log(entry);
}

Output:
["Tom", "Tom"]
["Mike", "Mike"]

gopal1996/ES6_Set.md

Set