To Test Camera, Microphone and Speaker through a .Net web application

I have built a .NET web application for video chat through OpenTok APIs, and want to give an option to the users to test their settings for camera, speaker and microphone after they log into my application, similar to as we have in Skype, go-to-meeting etc., except for Skype is a windows app and Go to Meeting comes in as a plugin with outlook. Is there a way to check if the below three are installed properly/ enabled on a computer/ laptop through some client side scripts (may be Java Script or something similar) on my web application:

1. Camera
2. Microphone
3. Speaker

Many Thanks!!