I just came across this online code editor. In my opinion this is far superior to codepen particularly when you get onto the bigger java script and react challenges.
linting (helps show errors)
syntax highlighting of error
shows react’s error messages in the html preview
much better console than codepen
I find when using codepen it swallows up errors and is difficult to debug. Take the time to get to know codesandbox.io and you will save yourself so much time.