Not the author, but you can find sources following the link: https://github.com/geon/geon.github.com/blob/master/_posts/2...

Basically - you leave first and last letters of the word where they are, and mix all other characters randomly at random times.

Just use "View Source" (Ctrl/Cmd + U) in your browser, the source is clear and not minified. Look for "messUpWords".