set.js

class Set {
  constructor() {
    this._items = {};
  }

  add(value) {
    if (!this.has(value)) {
      this._items[value] = value;
      return true;
    }
    return false;
  }

  remove(value) {
    if (this.has(value)) {
      delete this._items[value];
      return true;
    }
    return false;
  }

  has(value) {
    return this._items.hasOwnProperty(value);
  }

  clear() {
    this._items = {};
  }

  get size() {
    return Object.keys(this._items).length;
  }

  values() {
    return Object.keys(this._items);
  }

  union(otherSet) {
    let unionSet = new Set();
    let values = this.values();
    for (let i = 0, len = values.length; i < len; i++) {
      unionSet.add(values[i]);
    }
    values = otherSet.values();
    for (let i = 0, len = values.length; i < len; i++) {
      unionSet.add(values[i]);
    }
    return unionSet;
  }

  intersection(otherSet) {
    let intersectionSet = new Set();
    let values = this.values();
    for (let i = 0, len = values.length; i < len; i++) {
      if (otherSet.has(values[i])) {
        intersectionSet.add(values[i]);
      }
    }
    return intersectionSet;
  }

  difference(otherSet) {
    let differenceSet = new Set();
    let values = this.values();
    for (let i = 0, len = values.length; i < len; i++) {
      if (!otherSet.has(values[i])) {
        differenceSet.add(values[i]);
      }
    }
    return differenceSet;
  }

  subset(otherSet) {
    if (this.size > otherSet.size) {
      return false;
    } else {
      let values = this.values();
      for (let i = 0, len = values.length; i < len; i++) {
        if (!otherSet.has(values[i])) {
          return false;
        }
      }
      return true;
    }
  }

}