Set, Map, WeakSet, WeakMap

intersection.js

let union = ( set1, set2 ) => {
	return new Set([...set1, ...set2]);
}

let first = [1, 3, 1, 5, 7, 3, 9, 12, 15];
let second = [1, 20, 18, 5, 10, 3, 16];

union(first, second); /*? */

let intersection = (set1, set2) => {
	return new Set(
		[...set1].filter(elem => set2.has(elem))
	)
}
let set1 = new Set([1, 2, 3, 4, 5]);
set1.has(3); /*? */
let set2 = new Set([1, 3, 5, 7, 9]);
set2.has(3); /*? */

intersection(set1, set2); /*? */

let intersect = new Set([1, 3, 5, 6, 3, 10]);
let intersect2 = new Set([2, 6, 3, 15, 7]);
intersection(intersect, intersect2); /*? */

set.js

const myArray = [1, 4, 1, 3, 8, 4, 9, 12, 15, 8, 17, 20];

function removeDuplicates(arr) {
	return [ ...new Set(arr) ];
}

removeDuplicates(myArray);

union.intersect.difference.js

let union = ( set1, set2 ) => {
	return new Set([...set1, ...set2]);
}

let first = [1, 3, 1, 5, 7, 3, 9, 12, 15];
let second = [1, 20, 18, 5, 10, 3, 16];

union(first, second); /*? */

let intersection = (set1, set2) => {
	return new Set(
		[...set1].filter(elem => set2.has(elem))
	)
}
let set1 = new Set([1, 2, 3, 4, 5]);
set1.has(3); /*? */
let set2 = new Set([1, 3, 5, 7, 9]);
set2.has(3); /*? */

intersection(set1, set2); /*? */

let intersect = new Set([1, 3, 5, 6, 3, 10]);
let intersect2 = new Set([2, 6, 3, 15, 7]);
intersection(intersect, intersect2); /*? */

let difference = (set1, set2) => {
	return new Set(
		[...set1].filter(elem => !set2.has(elem))
	)
}
difference(intersect, intersect2); /*? */

weakMap

let _width = new WeakMap();
class Square {
	constructor( width ) {
		_width.set( this, width );
	}
	get area() {
		let width = _width.get( this );
		return width * width;
	}
	get removeArea() {
		return _width.delete(this);
	}
}

let mySquare = new Square(10); /*? */
mySquare.area; /*? */
mySquare.delete; /*? */