Too much temporary data and inefficient operations

[lzralbu]

Consider using the standard .values instead of the custom .toArray. Besides, I'd also suggest to use Set's methods as much as possible since it is implemented as a hashset, which is very efficient, instead of relying on Array's methods which usually take at least linear time.

For example, .intersection could be implemented along the following lines

intersection(s1, s2) {
  s3 = new Set();
  s1.forEach(value => {
    if (s2.has(value)) {
      s3.add(value);
    }
  });
  return s3;
}

[jpbulman]

@lzralbu That's a good idea! It's not entirely space efficient either. If you'd like to take this up and make a pr, feel free!