How does one install an extension for Chrome browser from the local file system?

Found a set of instructions online for loading your own custom extension:

• Navigate to chrome://extensions
• Expand the Developer dropdown menu and click “Load Unpacked Extension”
• Navigate to the local folder containing the extension’s code and click Ok
• Assuming there are no errors, the extension should load into your browser

What kind of extension is it? Is it a .CRX file? A (possibly ZIP’d) folder? A .JS user-script? The process differs for each.

• CRX:
  1. Drag and drop the .CRX file onto the page chrome://extensions
  2. Click the Install button in the prompt at the bottom of the screen
     
     
• Folder:
  1. If it is ZIP’d, extract the contents somewhere
  2. In Chrome, open chrome://extensions/
  3. Click + Developer mode
  4. Click Load unpacked extension…
  5. Navigate to the extension’s folder and click OK
  6. Delete the (extracted) folder (the extension was copied)
     
     
• User Script:
  1. Exit Chrome (all windows)
  2. Copy the .JS file to the User Scripts folder in your User Data folder
  3. Run Chrome