#2, might as well use an object... the "encode" is meaningless since it won't be a numeric comparison. may as well use `this["_" + word] = true;` prepending the underscore only to avoid use of reserved words, or overriding object prototypes.
#5 the linked list's "insert" doesn't account for middle-insert or changing current position.
The solution to question 4 part 2 is also a bit odd. Left a comment about that here: https://medium.com/@simon.kusterer/the-suggested-second-solution-of-question-4is-quite-odd-imo-3891ff46bfd6