Detect draft mode from Lua in LuaLaTex

Question

I'm working with a document for which I need to generate some data from a Lua script each time the PDF is produced. However, the generation of this data might be a slow, so I would like the script only to generate it from scratch when lualatex doesn't run in draft mode.

I wonder if there's something like this:

if tex.isRunningDraftMode() then
    print("USING OLD DATA")
else
    generateDataFromScratch()
end

Note that during the generation of the data, nothing is written to the document.

Answer 1

You can test for draft mode with tex.draftmode:

if tex.draftmode == 1 then
  print'draftmode'
else
  generateDataFromScratch()
end

Attention: this tests for the engine level draft mode (Triggered by running lualatex with the --draftmode option or the \draftmode primitive. In this mode LuaTeX does not generate a PDF at all).

If you are thinking about a different draft mode you will need another answer.