set.js

const Set = function() {
    let set = [];
    this.exist = function(element) { // check if element is in set return true, else return false
        return (set.indexOf(element) !== -1)
    }
    this.add = function(element) { // add element to set if not exist, do not add if it exists
        if(!this.exist(element)) {
            set.push(element);
            return `${element} is added to set!`;
        }
    }
    this.list = function() { // list all element in set
        return set;
    }
    this.remove = function(element) { // remove an element if it's in set
        if(this.exist(element)) {
            set.splice(set.indexOf(element), 1);
            return `${element} is removed from set!`;
        } else { return `${element} is not in set!`; }
    }
    this.length = function() { // return number of element in set
        return set.length;
    }
    this.union = function(setC) { // return the union set of two sets
        let union = new Set();
        let setA = this.list();
        let setB = setC.list();
        for(let i = 0; i < setA.length; i++) {
            union.add(setA[i]);
        }
        for(let j = 0; j < setB.length; j++) {
            union.add(setB[j]);
        }
        return union;
    }
    this.intersect = function(setC) { // return a set of intersection of 2 sets
        let intersect = new Set();
        let setA = this;
        let setB = setC.list();
        for(let i = 0; i < setB.length; i++) {
            if(setA.exist(setB[i])) {
                intersect.add(setB[i])
            }
        }
        return intersect;
    }
    this.difference = function(setC) { // return a set of difference of 2 sets
        let setA = this;
        let difference = setA.union(setC);
        let setB = setA.intersect(setC).list();
        for(let i = 0; i < setB.length; i++) {
            difference.remove(setB[i]);
        }
        return difference;
        
    }
}

const mySet = new Set();
console.log(mySet.add('a'));                    // a is added to set!
console.log(mySet.exist('a'));                  // true
console.log(mySet.exist('b'));                  // false
console.log(mySet.list());                      // [ 'a' ]
console.log(mySet.add('b'));                    // b is added to set!
console.log(mySet.add('c'));                    // c is added to set!
console.log(mySet.remove('c'));                 // c is added to set!
console.log(mySet.list());                      // [ 'a', 'b' ]
console.log(mySet.length());                    // 2
const mySet2 = new Set();
console.log(mySet2.add('a'));                   // a is added to set!
console.log(mySet2.add('g'));                   // g is added to set!
console.log(mySet2.add('h'));                   // h is added to set!
console.log(mySet2.list());                     // [ 'a', 'g', 'h' ]
console.log(mySet.union(mySet2).list());        // [ 'a', 'b', 'g', 'h' ]
console.log(mySet.intersect(mySet2).list());    // [ 'a' ]
console.log(mySet.difference(mySet2).list());   // [ 'b', 'g', 'h' ]