Years ago when browser compatibility required 100s of workarounds for each browser and version, it made sense to use a framework to hide the complexity and keep up to date. But with modern browsers this just isn't the case.
- update the view when changes from a backend data source arrive, either via some sort of polling mechanism or a persistent connection.
- allow the user to edit fields on the selected item.
- automatically save any pending changes when navigating away from the page.
AKA every CRUD app ever. You are going to need a framework (most commonly MV*) to deal with this in a maintainable way. Whether you use a vendor or create your own, you will end up with a framework.
Virtual list controls that need to manage thousands of items/rows.
Hint: you're going to need a custom scroll bar.
- take object of arbitrary depth {a: 1, b: [1, 2, {c: 3}]} and send as querystring parameters to Rails/Node/PHP/whatever backend
- take two parallel ajax calls and run some code when they're both done
- SPA w/ parameterized urls