I use these functions all the time for easing values, it uses JS and I made it so their usage is Math.functionName just for personal preference. This does not include ALL ease functions, just the ones that I have had use for. If you're interested in bounce, elastic, or other ease functions google is your friend.

https://vylocity.com/ide/Konlet/easeFunction

Functions included: (Most have in, out, and in-out functions.)
linear tween
quad
cubic
quart
quint
sine
expo
circ

Updated this today. Base usage is now JS.functionName. There is now a Math.ease function which evals any of the mathematic functions. Enjoy.

New easing functions:
Elastic
Back
Bounce

Usage example:
Math.ease('easeOutBack', 100, 0, 1, 100)

Math.ease(name, t, b, c, d)
name = easing method
t = current step
b = initial value
c = overall change (i.e., +1, -2)
d = total steps