background.html vs. background.js - chrome extension

Question

I am really confused here. I am trying to understand the file architecture of chrome extension. I am reading this doc: https://developer.chrome.com/extensions/overview#arch

My situation:

I want to setup the oauth flow so that user can log in inside the extension (the other endpoint is my django backend). Till now, I have these files:

background.js 
content.js
popup.html
manifest.json

where my content.js sends message to background.js and gets response back. so far so fine!

But now while reading the doc for oauth, i am confused not knowing what the background.html is. is it actually the file which should contain all js code of my background.js? but, if i change this in manifest to .html, like:

"background": {
"persistent": false,
"scripts": ["jquery111.js", "background.html"]

extension isnot working anymore. In OAuth doc, it says:

Place the four library files in the root of your extension directory 
(or wherever your JavaScript is stored). Then include the .js files in your 
background page...
Your background page will manage the OAuth flow.

but in the architecture doc, it says:

This figure shows the browser action's background page, which is defined by
background.html and has JavaScript code that controls the behavior of 
the browser action in both windows.

what is the difference between background.html and background.js?

Answer 1

You're only allowed to specify either an array of scripts...

"background": {
    "persistent": false,
    "scripts": [ "jquery111.js"]
}

... or a page, which can then reference the script(s) the page needs:

"background": {
    "persistent": false,
    "page": "background.html"
}

Your background.html page could in theory be nothing else other than a list of needed scripts.

<script src="jquery111.js"></script>

If you try to specify both, the extension won't load:

The background.page and background.scripts properties cannot be used at the same time. Could not load manifest.