ES6 class variable alternatives

Question

Currently in ES5 many of us are using the following pattern in frameworks to create classes and class variables, which is comfy:

Answer 1

If its only the cluttering what gives the problem in the constructor why not implement a initialize method that intializes the variables. This is a normal thing to do when the constructor gets to full with unnecessary stuff. Even in typed program languages like C# its normal convention to add an Initialize method to handle that.