From the documentation: Backbone.sync is the function that Backbone calls every time it attempts to read or save a model to the server. By default, it uses jQuery.ajax to make a RESTful JSON request and returns a jqXHR. The sync function may be overridden globally as Backbone.sync, or at a finer-grained level, by adding a sync function to a Backbone collection or to an … Read more
No, you can’t, though I would rely on the Screen object, not the URL https://codex.wordpress.org/Function_Reference/get_current_screen
It was introduced in 3.5 for the media library, but it’s been periodically updated since then. Honestly, it’s been around long enough that you’re almost certainly using something else that has a more recent requirement.
Is there a media_upload_tabs-similar filter to add tabs to the simple/featured image picker?
Mapping Backbone Models to serialized array in wp_options table
How to submit data between wp_iframe and backbone.js in media upload
Setting/unsetting terms using the Backbone JavaScript client
wp.template() returns tags in Ajax response
Accessing user Meta data via REST and backbone
rendering view in backbone