Here’s the disconnect. You’re expecting Atom to be able to parse your code and know that
t.a and company have meaning. Atom has no means of doing this built into it. It is a code editor, not an IDE, and all of the autocomplete packages I know of are nothing more than lists of keywords. Atom does have the capability to complete words that are found in the document you’re working in, but in order for it to do that, you have to start typing a word.
It sounds like you’re expecting Atom to be a drop-in replacement for Netbeans or Visual Studio, but with more flexibility. It is not. It has different strengths and being “dumber” regarding specific languages is a weakness.
I’m 90% sure that a package could solve this, but I don’t have any idea how it would go about doing that. You’d probably need for a compiler tool to not fully compile the code, but just spit out assigned variables into a list that could be referenced by the autocomplete dropdown.