Snippets of stuff that developers have learned that may be useful to other developers but is not yet sufficiently complete or structured for a dedicated page.
The WebUI is built on a 'single page application' framework called Ext JS. The version used appears to be 3.4.1.1 which, is considerably outdated (released circa 2009-2011).
A link to the Ext JS documentation can be found here: https://cdn.sencha.com/ext/gpl/3.4.1.1/docs/
The WebUI appears to be heavily dependent upon the internal idnode structures that not only supply the data to the WebUI via JSON, but also data type and formatting information. See the JSON Documentation for more details.
Each page or group of pages in the WebUI has its own JavaScript file, however, these normally contain just some setup and housekeeping functions specific to that area, all of the heaving lifting is done in idnode.js and tvheadend.js based on the idnode(s) in question.
Internally, TVH stores many objects in Red-Black tree structures rather than arrays. There are a number of preprocessor macros to support this. All of these macros are named RB_fn, for example, RB_FOREACH.
https://github.com/tvheadend/tvheadend/blob/master/src/redblack.h
https://en.wikipedia.org/wiki/Red%E2%80%93black_tree