Simple Easing Functions in Javascript - see https://github.com/gre/bezier-easing

easing.js

/*
 * This work is free. You can redistribute it and/or modify it under the
 * terms of the Do What The Fuck You Want To Public License, Version 2,
 * as published by Sam Hocevar. See the COPYING file for more details.
 */
/*
 * Easing Functions - inspired from http://gizma.com/easing/
 * only considering the t value for the range [0, 1] => [0, 1]
 */
EasingFunctions = {
  // no easing, no acceleration
  linear: t => t,
  // accelerating from zero velocity
  easeInQuad: t => t*t,
  // decelerating to zero velocity
  easeOutQuad: t => t*(2-t),
  // acceleration until halfway, then deceleration
  easeInOutQuad: t => t<.5 ? 2*t*t : -1+(4-2*t)*t,
  // accelerating from zero velocity 
  easeInCubic: t => t*t*t,
  // decelerating to zero velocity 
  easeOutCubic: t => (--t)*t*t+1,
  // acceleration until halfway, then deceleration 
  easeInOutCubic: t => t<.5 ? 4*t*t*t : (t-1)*(2*t-2)*(2*t-2)+1,
  // accelerating from zero velocity 
  easeInQuart: t => t*t*t*t,
  // decelerating to zero velocity 
  easeOutQuart: t => 1-(--t)*t*t*t,
  // acceleration until halfway, then deceleration
  easeInOutQuart: t => t<.5 ? 8*t*t*t*t : 1-8*(--t)*t*t*t,
  // accelerating from zero velocity
  easeInQuint: t => t*t*t*t*t,
  // decelerating to zero velocity
  easeOutQuint: t => 1+(--t)*t*t*t*t,
  // acceleration until halfway, then deceleration 
  easeInOutQuint: t => t<.5 ? 16*t*t*t*t*t : 1+16*(--t)*t*t*t*t
}

Great gist @gre!

I thought it might be helpful to those who wanted to extend the curves to see how that could be done using higher order functions and increasing the power (Thanks to @lindell for the original snippet! This version however removes the unnecessary Math.abs, reuses easeIn for the easeOut function and changes linear to reference easeIn rather than easeInOut to reduce the complexity for each call (although this definitely isn't an exercise in performance))

const easeIn = p => t => Math.pow(t, p)
const easeOut = p => t => 1 - easeIn(p)(1 - t)
const easeInOut = p => t => t < .5 ? easeIn(p)(t * 2) / 2 : easeOut(p)(t * 2 - 1) / 2 + .5
const Easings = {
	linear: easeIn(1),
	easeInQuad: easeIn(2),
	easeOutQuad: easeOut(2),
	easeInOutQuad: easeInOut(2),
	easeInCubic: easeIn(3),
	easeOutCubic: easeOut(3),
	easeInOutCubic: easeInOut(3),
	easeInQuart: easeIn(4),
	easeOutQuart: easeOut(4),
	easeInOutQuart: easeInOut(4),
	easeInQuint: easeIn(5),
	easeOutQuint: easeOut(5),
	easeInOutQuint: easeInOut(5)
}

Knowing this, you can re-write @gre's gist like so:

const Easings = {
	linear = t => t,
	easeInQuad = t => Math.pow(t, 2),
	easeOutQuad = t => 1 - Math.pow(1 - t, 2),
	easeInOutQuad = t => t < .5 ? Math.pow(t * 2, 2) / 2 : (1 - Math.pow(1 - (t * 2 - 1), 2)) / 2 + .5,
	easeInCubic = t => Math.pow(t, 3),
	easeOutCubic = t => 1 - Math.pow(1 - t, 3),
	easeInOutCubic = t => t < .5 ? Math.pow(t * 2, 3) / 2 : (1 - Math.pow(1 - (t * 2 - 1), 3)) / 2 + .5,
	easeInQuart = t => Math.pow(t, 4),
	easeOutQuart = t => 1 - Math.pow(1 - t, 4),
	easeInOutQuart = t => t < .5 ? Math.pow(t * 2, 4) / 2 : (1 - Math.pow(1 - (t * 2 - 1), 4)) / 2 + .5,
	easeInQuint = t => Math.pow(t, 5),
	easeOutQuint = t => 1 - Math.pow(1 - t, 5),
	easeInOutQuint = t => t < .5 ? Math.pow(t * 2, 5) / 2 : (1 - Math.pow(1 - (t * 2 - 1), 5)) / 2 + .5
}

Although it is much more verbose, hopefully it's easier to understand for those who don't understand the pre-decrement tricks

Finally you can take the previous example and substitute parts of the equations to reference each other (cleaning it up a little bit)

const linear = t => t
const easeInQuad = t => Math.pow(t, 2)
const easeOutQuad = t => 1 - easeInQuad(1 - t)
const easeInOutQuad = t => t < .5 ? easeInQuad(t * 2) / 2 : easeOutQuad(t * 2 - 1) / 2 + .5
const easeInCubic = t => Math.pow(t, 3)
const easeOutCubic = t => 1 - easeInCubic(1 - t)
const easeInOutCubic = t => t < .5 ? easeInCubic(t * 2) / 2 : easeOutCubic(t * 2 - 1) / 2 + .5
const easeInQuart = t => Math.pow(t, 4)
const easeOutQuart = t => 1 - easeInQuart(1 - t)
const easeInOutQuart = t => t < .5 ? easeInQuart(t * 2) / 2 : easeOutQuart(t * 2 - 1) / 2 + .5
const easeInQuint = t => Math.pow(t, 5)
const easeOutQuint = t => 1 - easeInQuint(1 - t)
const easeInOutQuint = t => t < .5 ? easeInQuint(t * 2) / 2 : easeOutQuint(t * 2 - 1) / 2 + .5

Great thread!

@aarongeorge thanks a lot! this is super useful! specifically, recently I was wondering how to generate it to any pow, I used this to something unrelated to easing but to do "distribution" => https://greweb.me/plots/109 (making my lines reaching more the edges)

@gre glad I could return the favour! Full credit to @lindell for the original Higher Order implementation. I just wanted to break it down and tweak a few things so it benefits more people.

An alternative (works somehow)

eval(function(p,a,c,k,e,d){e=function(c){return c.toString(36)};if(!''.replace(/^/,String)){while(c--){d[c.toString(a)]=k[c]||c.toString(a)}k=[function(e){return d[e]}];e=function(){return'\\w+'};c=1};while(c--){if(k[c]){p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c])}}return p}('f d={c:3(n){0 n},g:3(n){0 n*n},a:3(n){0 n*(2-n)},7:3(n){0 n<.5?2*n*n:(4-2*n)*n-1},9:3(n){0 n*n*n},b:3(n){0--n*n*n+1},e:3(n){0 n<.5?4*n*n*n:(n-1)*(2*n-2)*(2*n-2)+1},k:3(n){0 n*n*n*n},h:3(n){0 1- --n*n*n*n},i:3(n){0 n<.5?8*n*n*n*n:1-8*--n*n*n*n},l:3(n){0 n*n*n*n*n},j:3(n){0 1+--n*n*n*n*n},m:3(n){0 n<.5?6*n*n*n*n*n:1+6*--n*n*n*n*n}};',24,24,'return|||function|||16|easeInOutQuad||easeInCubic|easeOutQuad|easeOutCubic|linear|EasingFunctions|easeInOutCubic|var|easeInQuad|easeOutQuart|easeInOutQuart|easeOutQuint|easeInQuart|easeInQuint|easeInOutQuint|'.split('|'),0,{}))

visual cheat sheet https://easings.net/

This is really good but the easing functions are causing me trouble. I would like the first 75% of the count to go very quickly, and then decelerate to a crawl. I what would the proper function be for this? I imagine something like:

const easeOut = t<.75 ? t => t : [SOMETHING] ;

but I don't know what to put there.