In node.js how do you referance the directory below the current directory

I have a /custom_modules/db.js and am trying to require it from /routes/users.js but am unsure of how to do so.

You use ./ to signify local directory that you are in, and ../ to go back a directory. Therefore:

require('./../custom_modules/db');

Should just use ../ Example :

var db = require('../custom_modules/db.js');

Just insert a leading / to give an absolute path:

require('/custom_modules/db.jpg');

The rules for resolving modules path are detailed in the modules documentation.