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How Comfy loads custom nodes

When Comfy starts, it scans the directory custom_nodes for Python modules, and attempts to load them. If the module exports NODE_CLASS_MAPPINGS, it will be treated as a custom node.
A python module is a directory containing an __init__.py file. The module exports whatever is listed in the __all__ attribute defined in __init__.py.

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init.py

__init__.py is executed when Comfy attempts to import the module. For a module to be recognized as containing custom node definitions, it needs to export NODE_CLASS_MAPPINGS. If it does (and if nothing goes wrong in the import), the nodes defined in the module will be available in Comfy. If there is an error in your code, Comfy will continue, but will report the module as having failed to load. So check the Python console! A very simple __init__.py file would look like this:

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NODE_CLASS_MAPPINGS

NODE_CLASS_MAPPINGS must be a dict mapping custom node names (unique across the Comfy install) to the corresponding node class.

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NODE_DISPLAY_NAME_MAPPINGS

__init__.py may also export NODE_DISPLAY_NAME_MAPPINGS, which maps the same unique name to a display name for the node. If NODE_DISPLAY_NAME_MAPPINGS is not provided, Comfy will use the unique name as the display name.

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WEB_DIRECTORY

If you are deploying client side code, you will also need to export the path, relative to the module, in which the JavaScript files are to be found. It is conventional to place these in a subdirectory of your custom node named js.
Only .js files will be served; you can’t deploy .css or other types in this way
In previous versions of Comfy, __init__.py was required to copy the JavaScript files into the main Comfy web subdirectory. You will still see code that does this. Don’t.