Best JS API/Framework out there for new online App?

I know it’s a pretty general question, but I was wondering what’s everyones view on what are some of the best JS API’s/Frameworks out there for a new online App? I’m still undecided if whether it will need to be responsive, or if I’ll code a native version of the App but for now I’m just interested in learning about what my options are in regards to building an online App with JS.

Access to database functions are very important, and I’m already a fan of

Thanks for any help.

Is your question about server side or client side?
For client side, you can take a look at, where’s a good overview with examples on popular MVC frameworks. I personally used backbone.js+require.js for one project and, once managed to wrap my head around it’s main concepts, quite liked it.
As for serverside, depending on complexity I choose plain node.js or expressjs.

It’s interesting that you mentioned Backbone.js as I think that’s what the parse SDK uses.