Run npm install to install all dependencies.
Run node main.js path_to_file_a path_to_file_b. Absolute paths are preferred.
In your favorite editor, navigate to module main.js. You'll find wc.mode = 'SYNC'; which you may set to 'ASYNC'.
In case of SYNC, wordcount module uses fs.statSync() to get file information. In case of ASYNC, it uses fs.stat().