Selenium: strftime, sprintf

I would like to see a strftime or an sprintf in Selenium.

Javascript has a printf, but only for files, not for strings.
(Maybe there is a way to regards strings as files, but my Javascript competence is not good enough for that.)

I found Javascript code, that implements sprintf.

(I only introduced “Selenium” in the title, because the Tweet created from a title w/o it looks stupid.)