Comment #1 on issue 838 by l...@chromium.org: Function [[Call]] should  
return Reference Type
http://code.google.com/p/v8/issues/detail?id=838

This is correct. While V8 never has a function return a Reference, it would  
be against the spirit of ES5 section 16 to consider this an early error  
(unlike, e.g., the assignment "3=4").

The spec isn't entirely clear, due to the wording of the last case where  
Early Errors are required: "Attempts to call PutValue on any value for  
which an early determination can be made that the value is not a Reference  
(for example, executing the assignment statement 3=4)."
V8 can actually determine early that a function call isn't a Reference,  
because it never is in V8, but that seems counter to the intended meaning  
when reading the following sentence: "An implementation shall not treat  
other kinds of errors as early errors even if the compiler can prove that a  
construct cannot execute without error under any circumstances.".