Open up an old Java code base, and your IDE will tell you to refactoring tons of code, as it was written in an old way it thinks you shouldn't use anymore, uses

Open up an old Java code base, and your IDE will tell you to refactoring tons of code, as it was written in an old way it thinks you shouldn't use anymore, uses deprecated classes, etc. Javascript is even more dramatic, where it will tell you to fix every single variable declaration, as people decided "var" was a mistake, and there is a whole new way of defining classes.