I've looked at the various ways to embed a web browser into an application (like IE or Safari via OS-specific means, or Firefox/Mozilla via XULRunner, or Chrome via the Chromium Embedded Framework) and I've managed to integrate CEF with my app up to a point where I'm convinced that it'll all work as expected. Now, it seems to me that whenever I want to modify the DOM (e.g. to add or remove elements), I'll have to do this via Javascript, i.e. my application calls out to Javascript where the actual work is done.
I wonder why this is so. My (naive?) belief is that if for example I call appendChild in Javascript, the actual "work" of appending a child will eventually be performed by a C/C++ function as the browser itself is written in C/C++ and not in Javascript. So, I'm wondering why in an embedded web browser I can't call this C/C++ function directly instead of going through Javascript. I understand that for general scripting you don't want other languages than Javascript for security reasons, but if the browser is embedded into an application I can control anyway this shouldn't be the reason, should it?
What am I missing?
CEF is implemented as a layer between chromium's content api and your application. When using CEF, Chromium is a library inside CEF, and you only have access to CEF's Public API, which is more or less restricted to whatever chromium content api leverages (keep in mind no browser was created as an embeddable plugin and then evolved into an application, it was always the other way around). The content API was the way google engineers had to formalize some forms of introspection, but they aren't completed simply because the browser isn't completely modular by itself. There's work in progress on chromium code to separate specific "do-it-all" components in more general ones that you may pick at will.
Therefore you can't simply hook into chromium's implementation details when using CEF: you'd need to patch it to implement something it doesn't expose by itself. CEF implements a class for DOM traversal (see here), but you can only pick at DOM, not change it.
That said, on the C++ side you can do some arbitrary stuff such as inspecting/mangling http requests (which allows you to inject javascript into pages, for instance), and running arbitrary javascript code straight from C++, which can, by it's own turn, asynchronously call back to C++ code by diverse paths (ajax -> http handling in C++, or V8 extensions which you can code straightly in C++.
See https://bitbucket.org/chromiumembedded/cef/wiki/JavaScriptIntegration for more details.
One could customize CEF or go straightly to chromium source code, but that thing is huge. Other solutions I heard of are more or less alike in terms of API limitations, i.e. Awesomium, Mozilla's Gecko, etc.