I am using Express to handle a route which is in the format of /articles/:year/:month/:day, where year, month and day are optional.
The expressjs's guide to routing mentions:
Express uses path-to-regexp for matching the route paths; see the path-to-regexp documentation for all the possibilities in defining route paths. Express Route Tester is a handy tool for testing basic Express routes, although it does not support pattern matching.
Basically, you can use the ? character to make the parameter optional.
/articles/:year?/:month?/:day?