In your "Clear an array" section, you don't mention this:
Please look again.
Keep in mind that there is the Clear an array section, and then there are Clear an array - Round 2 and Clear an array - Round 3. Perhaps you were looking in one of the latter two.
At your quiz, you say "highlight text to see it", but then use a <spoiler> tag.
That's because I've configured spoiler tags to render as <div>, in my Display Settings. Probably I shouldn't say anything, and just let the user figure out how to deal with spoilers.
Your description of pop could be as detailed as your description of shift. Maybe put shift first and refer back to it.
I wrote it this way because I think of pop as being somewhat more fundamental, or intuitive, than shift. Clearly it could have been written the other way. A choice had to be made. :-)
I'm not sure "array slice" counts as jargon.
I think it's programming jargon, and frankly I've never heard the term used in relation to programming in any language other than Perl, though obviously it could be. The point was to introduce the reader to this term, which, if never encountered before would seem like jargon, and so ease the introduction by admitting that it's jargon.
Thank you for all your excellent comments.
A word spoken in Mind will reach its own level, in the objective world, by its own weight