Hi!
Thank you for your help guys!
I got it.
I didn't manage to get moment.js running like suggested by newt but because of your advice LuisCGForte to use full Javascript I found a post by Asmodean and got it working.
https://www.construct.net/en/forum/construct-3/how-do-i-8/convert-unixtime-readable-143677
Are you using C3 ?
C3 don't need the browser to exec JS, you can just right-click and add script directy.
But if you feel comfortable doing this, no problem.... i think only impact for minor performance