Challenge: Build a HTML/CSS/JS slideshow without libraries/frameworks/docs? OK!

I got most of the way. I needed MDN for checking the usage of:

• getElementsByClassName
• clearInterval and clearTimeout
• css transition syntax

The hard parts were off-by-1 errors and order of operations errors e.g. why does pressing the next button advance the slideshow 2 slides? Because the function that runs on an interval to advance the slideshow automatically already updated the slide index, but the new slide wasn’t displaying yet.

CodePen occasionally didn’t refresh when I expected it to, leaving some errors in the console for longer than I expected.

http://codepen.io/adamsullovey/pen/EajGPy