When I interview people for a position of Client-Side developer I try to figure out:
1) Understanding DOM (what is that, how is it related to HTML etc)
2) Understanding XML/namespaces
3) Understanding JavaScript (object-oriented? what otherwise)
4) Knowing approaches to componentization (XBL, HTC) - plus
5) Understanding OO principles
6) JavaScript closures
7) Memory leaks in browsers
The only simple test case I give right away:
I suggest interviewee to explain in technical terms that line.
And I also check on overall awareness of the current state of the Web technologies, among other questions I suggest designing a web-browser where interviewee is suggested to pick technologies he would put into his brand-new creature, suggest ones that might be missing from the current client-side platform.
