Learn how to create and use module plugs in Phoenix for organized, reusable middleware functionality.

What’s a module plug?

A module plug is a reusable module in Phoenix that processes each request, typically for more organization and code reuse than function plugs.

In this episode

• Builds a form for users to select their preferred console (PC, Xbox, PlayStation, Nintendo)
• Creates a SetConsole module plug that:
  • Reads the console selection from the URL or cookies
  • Assigns the selected console to the connection (so the choice is available in views)
  • Saves the console choice to a cookie for persistence between page reloads
  • Uses a default console if none is provided
  • Includes validation: only allows valid console names; falls back to default if invalid
• Shows how to wire the module plug into the Phoenix router pipeline for all browser requests
• Makes sure assign and put_resp_cookie are imported from Plug.Conn
• Console selection is reflected on all pages; invalid values do not pollute cookies or assigns

Best practice highlight

Using guards and pattern matching, only valid console choices are accepted for assignment and cookies; others revert to the default.

Why use module plugs?

• Keeps code more organized and maintainable (usually kept in a plugs/ folder)
• Preferred for most structured or multi-function plug logic

Summary

This video demonstrates building a stateful feature (selected console) for web visitors using module plugs, cookies, and assignment in Phoenix—covering common edge cases and best practices for plug architecture.