https://nodejs.org/dist/latest-v8.x/docs/api/fs.html#fs_fs_chmod_path_mode_callback https://nodejs.org/dist/latest-v9.x/docs/api/fs.html#fs_fs_chmod_path_mode_callback The "mode" value on the web is a "whole number". But sometimes you need an "octal". "number is the correct type in javascript. Thank you.