Hi, 
starting from version 0.20.2 (released yesterday) of tree-sitter-javascript 
the "function" primary expression has been renamed to "function_expression". 

The attached patch (for emacs 29) supports the old and new versions.
I also have a version for emacs 30.

Thank you. 
V.


-- 
Vincenzo Pupillo
Direzione ICT
Università degli Studi di Milano / University of Milan (Italy)
Via Giuseppe Colombo, 46, 20133 Milano