Uncaught TypeError: Cannot read property 'x' of undefined that end up taking lots of time to debug. The language does not help you catch these errors early enough in the development cycle, and they usually end up being discovered too late, mostly by your users reporting that something is not working.
What if you could release your web app with the confidence that you would never get any runtime exceptions again? What if every time you needed to refactor code, you could do it confidently knowing you have a compiler that would let you know of any errors and suggestions on how to fix them? What if you could get all these benefits today, right now?
Welcome to the world of Elm.