It is : https://developer.bluetooth.org/gatt...vicesHome.aspx
and more details here : https://developer.bluetooth.org/gatt...heart_rate.xml

If you don't yet know this website, you can bookmark it. It is the official developer documentation, listing all profiles, services, descriptors and characteristics, and is really well done : https://developer.bluetooth.org/gatt/Pages/default.aspx

For the NodeJS or Jolla specifics, I can not help however, I have only used it a bit through Qt Bluetooth libs found in newer releases (with mixed results) on other targets.