I am a front-end developer but I don't know any JavaScript mv* frameworks. It seems like most front-end job positions are now requiring experience with Backbone Ember etc. etc.<p>I've started learning Ember but I am curious, what would be an acceptable level of knowledge to have before I apply for a mid-level developer position?
I think if you have experience with JS in general and also experience with non-JS MVC frameworks you should be fine. The JS MV* frameworks are new and it would be ridiculous to assume that someone needs to know that if they are an otherwise qualified candidate. Still, why wait for an employer to require you to use them? Start a project (even if its pointless) to teach yourself! Not only does it teach you the technology but employers like to see that you like to do that kind of work for fun and are passionate about learning new things.