I get pretty annoyed when I see people dismissing client-side engineering as being somehow less challenging than server-side development - on the server, you only have to get it working on one platform (and for all but the most high traffic sites you can write code as badly as you like without much penalty). Client-side engineers have 5 different rendering engines to deal with, need to think about performance, accessibility, resizing, legibility... and that's before you even get to the huge domain that is modern JavaScript.