Is It Possible To Access Class Properties Without Initialising The Class?

I want to access all of the properties of a class that will be defined when the constructor is called, so that I can implement a sort of interface for the class. Say I had a class

Solution 1:

In this situation, is it possible to access hello?

Not without using a JavaScript parser (like IDEs do to try to infer instance mbmers). hello, as you say, doesn't exist as a property until/unless an instance is created. With a parser, you can (usually) determine what the property names will be, perhaps sometimes their initial values, but that's all.