That's how I did several interviews a while back. Before everyone somehow knew and loved BackboneJS, I took a functioning data-driven sorted table app, removed some of the model and controller code, left the view, and then asked them to complete it.

People either:

- Hacked together the internals to make it function, never considering any of the existing Backbone or _s functions

- Figured the existing code was a template, and rewrote it all now they thought it should've been (which can be good or bad)

- Learned enough of Backbone to complete the example with minimal code, but generally took longer because they had to learn the tool first

As a result, I got a great hire that knows when to refactor, when to leave existing code alone, and when to use AngularJS instead of Backbone!