I released Page.REST(https://page.rest#prerender) couple of weeks ago. It will pre-render JS based sites - so you can then extract rendered content using CSS selectors.
// URL to screenshot
service.prerender.cloud/screenshot/https://www.google.com/
// URL to pdf
service.prerender.cloud/pdf/https://www.google.com/
// URL to html (prerender)
service.prerender.cloud/https://www.google.com/