Gets a timing function from a "transition-timing-function" string

gistfile1.js

// Gets a timing function from a "transition-timing-function" string
// Written by Peter O. in 2012, released to the public domain
// Returns the function itself if the object passed in is a Function object,
// or the "ease" function if the object is null or undefined
// This file is in the public domain. Peter O., 2012. http://upokecenter.dreamhosters.com
// Public domain dedication: http://creativecommons.org/publicdomain/zero/1.0/
function getTimingFunction(f){
 if(typeof f=="undefined" || f==null)f="ease";
 if(typeof f=="function" || (f && f.constructor==Function))return f;
 if(f=="step-start")return function(v){ return (v>0) ? 1.0 : 0 };
 if(f=="step-end")return function(v){ return (v<1) ? 0 : 1.0 };
 if(f.indexOf("steps(")==0){
  var e=(/^steps\((\d+)\s*\)$/).exec(f);
  if(e){
   var s=parseInt(e[1]);
   if(s>0){ return function(x){ return Math.floor(x*s)/s } };
  }
  e=(/^steps\((\d+)\s*,\s*(start|end)\s*\)$/).exec(f);
  if(e){
   var s=parseInt(e[1]);
   if(s>0){
    if(e[2]=="end")return function(x){ return Math.floor(x*s)/s };
    return function(x){ return Math.ceil(x*s)/s };
   }
  }
  return function(v){ return v };
 }
 var bez=[0,0,1,1];
 if(f=="linear")bez=[0,0,1,1];
 else if(f=="ease-in")bez=[0.42,0,1,1];
 else if(f=="ease-out")bez=[0,0,0.58,1];
 else if(f=="ease-in-out")bez=[0.42,0,0.58,1];
 else if(f=="ease")bez=[0.25,0.1,0.25,1];
 else if(f.indexOf("cubic-bezier(")==0){
  var e=(/^cubic-bezier\((\d+(?:\.\d+)?)\s*,\s*(\d+(?:\.\d+)?)\s*,\s*(\d+(?:\.\d+)?)\s*,\s*(\d+(?:\.\d+)?)\s*\)$/).exec(f);
  if(e){
   bez=[parseFloat(e[1]),parseFloat(e[2]),parseFloat(e[3]),pars];
  }
 }
 return function(v){
  var t=0.5;
  var interval=0.25;
  var mt=0;
  if(v<=0)return 0.0;
  if(v>=1)return 1.0;
  for(var i=0;i<50;i++){
   mt=1-t;
   var x=3*mt*mt*t*bez[0]+3*mt*t*t*bez[2]+t*t*t;
   var diff=x-v;
   if(Math.abs(diff)<1.1920929e-07){
    break;
   } else if(diff>0){ // too far to the right
    t-=interval;
   } else { // too far to the left
    t+=interval;
   }
   interval/=2.0;
  }
  mt=1-t;
  var y=3*mt*mt*t*bez[1]+3*mt*t*t*bez[3]+t*t*t;
  if(y<0)y=0; if(y>1)y=1;
  return y;
 }
}