I showed a few people who have no idea about programming whatsoever how to hack websites to download .mp4 or .mp3 from source code of the website. How would you show them that using DOM...
You can use dev tools to view the network tab to find whatever URL Pandora is using.
You can use dev tools to find a media elements src attribute.
To see the JavaScript sources... You check the dev tools.
If anything, in the days of JavaScript, the HTML source will missing a few things.