Yes, you can understand a 10+ year old web app's JavaScript, but that's because there was very little JavaScript on it to begin with. I used to write a lot of

Yes, you can understand a 10+ year old web app's JavaScript, but that's because there was very little JavaScript on it to begin with. I used to write a lot of jQuery, and in my experience once the code on a page became longer than ~500 lines, it became significantly more difficult to wrap one's head around. With the new tools the baseline for understanding the code is higher, but if you meet that baseline then you can grok code that is much more complex.