Unfortunately, full networking capability as it exists in a typical virtual machine (like Virtualbox), will not be possible in pure javascript. Security featur

Unfortunately, full networking capability as it exists in a typical virtual machine (like Virtualbox), will not be possible in pure javascript. Security features of the browser like the same origin policy restrict this from being possible. Even if you were to use some of the exceptions to the same origin policy, you will be limited to sending HTTP requests. There is no way to send a UDP packet from javascript for example. Of course you can create browser extensions which expose these utilities, but then you're taking the easy way out :)