Common and Uncommon Mistakes in Development
We all make mistakes in the web development, some are common, some are uncommon, some are even stupid, but we should not be shame to share them. Write them down, and hopefully we don't make the same mistakes again.

This seems to be very easy one, but never do x.innerHTML += y, because it will disable all Javascript event predefined. Use document.body.appendChild(Elm) instead.
vanilla javascript
The first parameter in onClick function is "event", so if you want to pass other props, then make sure don't define them as the first parameter.