Web apps (web sites) are very powerful tools, however "background location" does not work with them.
Background Location Broadcaster is a tool, which lets the user send the location, to web apps (URIs), continuously in the background. Note 1! Only a few sites can be used with the app: List of controllable sites.
Note 2! The device (Android OS) can at any time close down any apps (including this app) because it wants to use its resources for other things. If the phone is connected to power, and doesn't run any other apps, it seems to be running for about 4-5 days before it is closed down.