# Return the HTML or image (png) of the javascript-rendered page in a local file
#
# The suggested use-case for this is rendering a widget
#
# TODO Test if container is running
# TODO Enable passing in of an htmlwidget and use saveWidget
#
# @md
# @param splash_obj Object created by a call to [splash()]
# @param file_path Absolute path to a filename on the local host. **This only works with a locally running Splash instance started with [start_splash]().**
# @param wait seconds to wait
# @param output either `html` or `png` to get the page content or an image capture
# @param viewport View width and height (in pixels) of the browser viewport to render the web page. Format is "`<width>x<height>`". e.g. 800x600. Default value is 1024x768.
# @param ... other params to [render_html()] or [render_png()]