Custom Lovelace Card: Custom element doesn't exist

I have created a custom card and placed it here:
\config\www\custom_card.js

I have added it to resources (through the UI) as:
/local/custom_card.js
Type: JavaScript module

I have restarted Home Assistant and performed an “Empty Cache and Hard Reload” in Google Chrome, yet I am still getting the “Custom element doesn’t exist…” error when this card is added to my dashboard:

type: entities
entities:
  - entity: fan.master_bedroom_fan
    type: custom:custom_card
    name: Fan

What am I missing?