Wrote an entire WebKitToHtml system previously, but should have used available open source projects like so. Live and learn and take some time to consider alternatives before committing to a plan.
Python option
https://github.com/paulhammond/webkit2png/
JavaScript Chrome Extension Chrome Store link
https://chrome.google.com/webstore/detail/full-page-screen-capture/fdpohaocaechififmbbbbbknoalclacl
Project code link
https://github.com/mrcoles/full-page-screen-capture-chrome-extension
Or use Vivaldi browser which has built in screen capture system.