fixed the issue. Will look into that further Fat arrow functions capture the this keyword relatively to what it is in the context they are declared in (for the second one this is the window). As for the third one, it might be because x() in an object literal is a shorthand for x: function()?
wish of those help Without documentation, or inspecting the source of the function executing the callback, you wont easily know. However, you can intercept them with some exploratory code and see what you get: