For front-end developers there are some ways to gauge his skill and experience:
Considering that front-end developers usually have worked with things that are clearly visible, it's not difficult for them to give up a list of websites that they've worked on.
One could argue that they can't due to non-disclosure agreement, but it is also not uncommon for them to have portfolio websites that you can check.
If they can't show off what they've done or what they can do then I'd be fairly suspicious. It's so easy to create projects on the Internet today (with tools such as jsfiddle, github, etc.) that it's inexcusable for a front-end developer to not do so.
This is generally what you should ask for prior to the interview so you can examine the material. That way you can have a two-way conversation and discussion with the candidate on how he works. If the candidate is unable discuss his work then it's a clear red flag.
The drawback with this exercise is that it takes time both for you and your candidate to sit this through to completion (and still may not lead to a hire if the candidate is right but decided to go elsewhere).