Very basic set-like collection, supporting only contains/add/remove.

simple_membership_set.js

function is(a) {
  return b => a === b;
}

function isNot(a) {
  return b => a !== b;
}

class SimpleMembershipSet {
  constructor(values = null) {
    this.values = values || [];
  }

  contains(v) {
    return this.values.find(is(v));
  }

  add(v) {
    if (!this.values.find(is(v))) {
      this.values.push(v);
    }
  }

  remove(v) {
    this.values = this.values.filter(isNot(v));
  }
}