Is there a way to detect a multi touch event on the screen through JavaScript for web apps?

Trying to make an overlay appear on a single touch event on a canvas, that tells the users that multi touch is needed to move the content within this canvas.

Can't seem to find anything at first glance, closest I could find is double tap but is not exactly what I want, any ideas?

Thanks in advance.

EDIT: Worth mentioning that I'm capable of making the overlay appear on a single tap, but I need some way to recognize multi touch and not double taps.