Lists and objects

So an array is an ordered list: square brackets, items fetched by position, and a built-in .length that always knows how many there are. One variable, forty books, no book40.

But a book isn't just a title; Sam also wants to know whether she finished it. For that there's a second shape: the object, a labelled box. { title: "Dune", finished: true } keeps each fact behind a named key, and a dot reaches in: book.title. Put the two shapes together and you get the structure underneath almost every app ever built. Look at it before we name it.