Takes two argument, self and other, and returns a new object of the same type as self which contains the elements that are in self but not in other.
self
other
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/difference
Takes two argument,
selfandother, and returns a new object of the same type asselfwhich contains the elements that are inselfbut not inother.