Another is when dealing with global variables people put on window. Instead of going window.logger, say in the case of log4javascript, you can instead just use logger since it’s global. HOWEVER, in larger applications where you’re dealing with race conditions, say some Backbone View’s expecting to have references to Models that haven’t been instantiated yet… you can safely test for those globals via typeof and fall back with logging statements in production code. If you don’t, you’ll get a null pointer.

Seems benign, but it’s not when refactoring spaghetti code that you want to ensure doesn’t break one thing when you fix another.