jQuery transition plugin with fallback to animate()

jquery.transition.js

(function ( $ ) {

  // What: a jQuery plugin for CSS3 transitions with animate() fallback
  // Author: kiur@node.ee
  // License: Public Domain

  var CSS3_TRANS_SUPPORT = (function() {
    var b = document.body || document.documentElement;
    var s = b.style;
    var p = 'transition';
    if (typeof s[p] == 'string') return true;
    v = ['Moz', 'Webkit', 'Khtml', 'O', 'ms'],
    p = p.charAt(0).toUpperCase() + p.substr(1);
    for (var i=0; i<v.length; i++) {
       if (typeof s[v[i] + p] == 'string') return true;
    }
    return false;
  })();

  $.fn.transition = function(newCSS, context, duration, easing, callback) {

    if(!CSS3_TRANS_SUPPORT) {
      this.animate(newCSS, duration, callback);
      return;
    }

    var self = this,
      context = context || 'all',
      duration = duration || 500,
      easing = easing || 'linear',
      key, val;

    var oldTransitionStyle = {
      '-webkit-transition': this.css('-webkit-transition'),
      '-moz-transition': this.css('-moz-transition'),
      '-ms-transition': this.css('-ms-transition'),
      '-o-transition': this.css('-o-transition'),
      'transition': this.css('transition')
    }

    var transitionStyle = context + ' ' + duration + 'ms ' + easing;
    for (key in oldTransitionStyle) {
      if(oldTransitionStyle.hasOwnProperty(key)) {
        this.css(key, transitionStyle);
      }
    }

    for (key in newCSS) {
      if(newCSS.hasOwnProperty(key)) {
        if(newCSS[key].indexOf('+=') === 0) {
          newCSS[key] = parseInt(this.css(key)) + parseInt(newCSS[key].substr(2));
        }
        else if(newCSS[key].indexOf('-=') === 0) {
          newCSS[key] = parseInt(this.css(key)) - parseInt(newCSS[key].substr(2));
        }
      }
    }

    this.css(newCSS);
    setTimeout(function() {

      self.css(oldTransitionStyle);
      callback && callback();
    }, duration);

    return this;

  }

}( jQuery ));