gistfile1.js

// t: current time
// b: beginning value
// c: change in value
// d: duration

var elast = function (t, b, c, d) {
  var s=1.70158;var p=0;var a=c;
  if (t==0) return b;  if ((t/=d)==1) return b+c;  if (!p) p=d*.3;
  if (a < Math.abs(c)) { a=c; var s=p/4; }
  else var s = p/(2*Math.PI) * Math.asin (c/a);
  return a*Math.pow(2,-10*t) * Math.sin( (t*d-s)*(2*Math.PI)/p ) + c + b;
}

var x = 100,
    t = 0;

for (var i = 0; i < 100; i++) {
  console.log(
    elast(t++, x, -1 * x, 100)
  );
}