In addition to browsers, there is nothing more, because the JS engine (for example, V8 in Chromium) and the API (DOM, BOM and others) are engaged in JavaScript. HTML parsing still makes sense to do a separate library, so there are such. With a big stretch - CSS. But JS with all APIs - that’s for sure the browser.
There are browsers that support the work of "offscreen", that is, without rendering (although it is always possible to have a crutch of the type to remove the window off the screen, etc.)
In Delphi, you can use the standard TWebBrowser, but this is a Donkey with all the consequences. Even in Delphi, you can precisely use CEF through the dcef3 shell, it is better, but I also didn’t like it, there are rough edges, it is suitable only for such tasks, namely for the Web UI, I did not use it.
And it is better to work immediately with those technologies that will be useful more than once.
Rulit, perhaps, Awesomium, but it is only for .NET.
So, IMHO, ideally, you would not only master the "new" for you "browser elements", but also switch to a new language.
After all, browsers are far from the only problem that is easily solved on .NET and with difficulty - on Delphi, with a rich past, but a dull present.
Alas.
Although, dolphists are still in demand, but usually on old projects.
For why write a new one on it? As a rule - no need. Alas again.
IdHTTP- will not perform javascript. "without the use of browser elements" - why such a restriction? - IgorЧто есть сейчас: локально сохранённая html страница с js, меняя в которой некоторые параметры получаем разное содержимое- are you sure that this will work? checked? - Zam