Java script/function to determine what day it is

We are creating a flow in conjuction with a screen to allow users to kick off a flow at their convenience (without have PFI installed on their computer).  The screen will have selection criteria for M-F and the users will be able to select which days they want to run it on.

The flow itself will run daily and check the appropriate flags to see which days it fully execute.  So basically I need to know what java script function will check what day it is so that I can do a comparison.  Example would be great.

Thank you