It would be useful to be able to load Javascript files before taking a screenshot

[larsmagne]

There's already the --javascript option, but if you're adding a lot of JS, you run into command line lengths problem.

My usecase is that I want to remove cookie banners and other annoyances, so I've converted various block lists to JS. This leads to 4MB of generated JS to run, so it's not practical to pass that in on the command line.

So a --javascript-file option would fix the issue.