Solid cross-browser compliant code. You enjoy hanging out on Quirksmode. Deep understanding of JS and how to make things dance with frameworks like Jquery. Have a solid background with one server-side language (PHP, Ruby, Python etc) and have a lot to show with it. Understand what a HTTP request is. Understand what AJAX really is. Security: Know about SQL injection and CSRF. As a experienced web dev, I think thats a good place to start. There's a lot to know actually, usually takes 3-4 years for someone to even get decent.