A powerful feature of this extension is that the same code can be used both client and server side, reusing implementations of the same code in PHP for server side and js client side.
A possible use case is for providing server and client side validation using the same JS code. Client side, the code would be run in the browser, and server side it’s executed using V8JS.
Other potential uses could be templates or any other business logic that’s needed both client and server side.
It seems like you’ll still be in uncharted territory here, though. I haven’t seen any libraries use V8JS for anything like this.
One of the ways I am using JS integration within PHP is to provide a simple manner for end users to safely execute user-supplied code (a.k.a. scripts) within a PHP-based app. With the implicit isolation, one can limit the inputs and functions available to protect both user privacy and system security while allowing a wide range of user-defined scripted actions within the server context.
In the core language and V8, nothing is asynchronous.
Sorry to bump / add to an ancient question, but a fairly obvious use case in the Web 2.0 / 3.0 era is going to be “when file_get_contents() just won’t cut it.”