[Sample from GPT-3; condensed paragraphs & formatting added for legibility inside popups, as the original plain text dumps strip the original HTML formatting of tutorials etc.]

Working with an example—rotating through an array For a number of years, I’ve been fascinated by the idea of writing code that can rotate through an array. Let’s say I have the following array of numbers:

            var myNumbers = [1, 2, 3, 4, 5];
          

            for (var i = myNumbers.length - 1; i ≥ 0; i-- ) { console.log( myNumbers[i] ); }
          

We know that the index of an array can be used as a “pointer” to the location in memory that contains a particular item in an array. If the array myNumbers has five items, then myNumbers[0], myNumbers[1], myNumbers[2], myNumbers[3] and myNumbers[4] will point to the values 1, 2, 3, 4 and 5 respectively.

In the previous example, the code starts with the length of the array (5) and subtracts one from it. As we know that index 0 in an array contains the first item in the array, the previous code will execute the following steps: Take the length of the array (5) Subtract 1 (so we now have 4) Start at the index that contains the first item in the array (myNumbers[4] = 3) and run down the array until we reach the last item in the array (myNumbers[3] = 5) So the above code will end up displaying the items in the array in reverse order, starting at index 4 and working backwards to index 0. At this point, we have a good idea of how we can access the values in an array in a specific order, but how do we go the other way?

It would be great if we could simply use the same code as above, but add a “–” operator before the last number. That way, we could add a simple parameter to the code to control the range of numbers it will use. Unfortunately, we can’t do that. While JavaScript will happily work with –, it will also happily take – in code and convert it to −1, or the last number in an array. That’s not going to do us any good, as we want the code to be flexible enough that we can work with a number that we specify as the range of numbers.

            function rotate(numbers, direction, number) { numbers.reverse(); numbers.push(number); numbers.unshift(number); };
          

The rotate function above has three parameters, and will rotate the values in the numbers array…