mjhjmtu

I am trying to encapsulate logic to determine if a button is visible inside the second argument via anonymous function:

component.set("!v.assignButtonVisible", function() 
 console.log('Do we get here?');
 return false;
);

However, the code inside the function never executes and the attribute is set to true.

The only reason I can think of is at run-time, when function() ... resolves, it is not null and therefore is interpreted as true.

Is what I'm trying to do possible? Can I call a named or anonymous function to get the value I'm looking for, or is my only option to create and set a var before calling component.set( ... )?

You actually put the function in to the attribute, not the return value, because the function was never "called" (executed). If you want to call such a function inline, you can, but you need to actually call it. This just requires a few more parentheses:

component.set("!v.assignButtonVisible", (function() 
 console.log('Do we get here?');
 return false;
)());

We put the entire function inside parentheses, then give it an empty parameter list. That pattern looks like:

(function(...) ... )(...)

You can put stuff in where the dots are (parameters and code body). This is called the "self-executing anonymous function" pattern.