ExpressJS dynamically generated pages - will search engines create listings based on query parameters?
Short answer, no. Search engines may be able to discover new pages by incrementing methods, but it is not an expected or predictable behaviour.
The easiest solution would a page linking to all other pages, thus allowing search engines to discover them.
Once these pages are indexed, visitors should be able to access a page with a URL like "http://www.example.net/location?zip=10001" by the keywords "Companies in New York City".
I would suggest you to also generate a sitemap with this module and the list of your zip codes.