As a developer of some "popular" widgets, I owe a great deal to ExtJS because it taught me that encapsulation, especially in JavaScript, a scripted language with defacto accessible source code, is just absurd. A simple thing like that reminded me of functional programming and the rest is history.

Extending a dropdown component meant that i had to copy some closure just to change a number in a wrapped function, and then update the copy-paste with each extjs version that touched it. Why? Because the developer didn't know any better. Similarly now you have "private" fields in classes, etc because some group wants them, because other languages have them so ofc JavaScript needs it too. When all you have is a hammer...

ExtJS is very much rooted in me as a "not like this", as much as Douglas Crockford is preaching a "keep it simple, stupid, like this". I get pleasure just by hearing him give a talk and saying that while they kids are adding and adding to this pretty ok language, he only needs tail call optimizations, because keeping to the good parts is more than enough.