Sample CO₂ Meter Chrome Extension

The extension uses WebHID to access a device for measuring the CO₂ level and temperature in your surroundings.

Testing the extension

1. Follow the instructions to load an unpacked extension.
2. Connect the CO₂ meter (currently it only supports the CO2Mini Indoor Air Quality Monitor from CO2Meter.com).
3. Open the extension popup window and click “Settings” button to go to the settings page.
4. Click the “Grant CO2 meter permission” button and grant the permission to the CO₂ meter.

Following the above steps, the device connection session to the CO₂ meter will be created when the extension is running. The input reports from the device will be processed and are visble from the popup window or settings page.

Design

• co2_meter.js: A CO2 meter device driver layer that uses WebHID to communicate with the device.
• co2-state-iframe.js: A module to be embedded in a regular page or popup window for showing the current CO2 meter status. It listens for events from the extension service worker, such as meter readings or availability, and renders the results.
• popup.js: For the extension popup window. It includes co2-state-iframe.js and a link to open main-page.js.
• main-page.js: The settings page for opening a popup to grant permission to the device. It includes co2-state-iframe.js as well.
• background.js: The script that runs on the extension service worker. This is the central piece of this extension, and it will:
  • Initialize the CO2 meter for starting to generate reading input reports using co2_meter.js.
  • Broadcast events (e.g., CO2 readings, CO2 availability) to registered clients (e.g., the popup window).

WebHID limitations in extension service workers

WebHID will be officially available to extension service workers in Chrome 115. Before M115, it can be enabled through the flag chrome://flags#enable-web-hid-on-extension-service-worker. However, there are limitations to the support for WebHID in extension service workers:

• Before M115 with flag enabled, if the service worker is idle for longer than 30 seconds it may be terminated, closing the device connection session. This limitation will be resolved in M115.
• Device connection events are not fired if the device is plugged or unplugged while the service worker is inactive. We have crbug.com/1446487 to track the resolution of this limitation. If your extension encounters issues because of this limitation, please leave a comment in the bug about your use case and how the limitation affects your extension.