Generic linear animation function

basicAnimate.js

window.animate = (function () {
  function animate(initialValue, finalValue, duration, callback, ease, startTime, currentTime) {
    if (startTime) {
      if (currentTime - startTime >= duration) {
        callback(finalValue);
        return;
      }
      callback(ease(currentTime - startTime, initialValue, finalValue - initialValue, duration));
    }
    window.requestAnimationFrame(function (currentTime) {
      startTime = startTime || currentTime;
      ease = ease || animate.easingFunctions.linear;
      animate(initialValue, finalValue, duration, callback, ease, startTime, currentTime);
    });
  }

  animate.easingFunctions = {
    linear: function (t, b, c, d) {
      return c * t / d + b;
    },
    inOutQuad: function (t, b, c, d) {
      t /= d / 2;
      if (t < 1) return c / 2 * t * t + b;
      t--;
      return -c / 2 * (t * (t - 2) - 1) + b;
    },
    // find more functions at http://gizma.com/easing/
  }

  return animate;
})()