Lua script in Splash - direct file download by button click

Question

How to directly download and save a file by button click using Splash Lua?

Example page and the download button:

Conditions:

• The download URL is generated dynamically upon button click
• Clicking the button will open a "Save As" prompt window to save the Excel file
• I am using a Splash docker service on localhost:8050. I write Lua script directly on the page.

I have searched the official docs about binary download, but the closest things I have managed to find were html:jpeg, html:png and response.body, which didn't quite seem to hit the mark. I also found no explicit examples or tutorials on Youtube.

Note: Please do not give workarounds such as using Selenium. I am only interested in how to do it with Lua.