CodePen has supported JSX syntax for a while now, through using Babel as the JavaScript preprocessor. Butttt, the syntax highlighting was a little janky. An opening HTML tag would be a totally different color than a closing tag, for example. Because the normal JavaScript syntax highlighting didn't really know what to do with that.

Thankfully, the latest release of CodeMirror shipped with a JSX mode, so we hopped right on that.

Syntax now looks correct in the Editor:

As well as in embeds:

Remember: you don't have to use JSX while using Babel, you just can if you want.