Audit for catching "classic" js framework mistakes #173
Description
As JavaScript is dynamically typed it usually won't error if you try to set the contents of an HTML element / text to something that isn't a string, which can be a classic mistake especially with frameworks like React and Vue: https://stackoverflow.com/questions/42308244/get-promise-value-in-react-component
I don't expect this'll be common, but since we're visiting and loading pages it should be very cheap for us to do a check across the text of the entire document for stuff like [object, null, and undefined as these are not really common outside of code.
We should start with [object because that is pretty much always a bug, and other values like null and undefined will need to try and avoid matching content within <script> tags