I’m in the process of developing a new blog theme for myself. I was trying to use CSS3 transitions but I wanted to fall back to JavaScript if transitions weren’t supported. I really want to avoid Modernizr if I can so I needed a quick and dirty test for detecting them. Here’s what I came up with:

var Detect = (function () { 
  function cssTransitions () { 
    var div = document.createElement("div"); 
    var p, ext, pre = ["ms", "O", "Webkit", "Moz"]; 
    for (p in pre) {
      if (div.style[ pre[p] + "Transition" ] !== undefined) {
        ext = pre[p]; 
        break; 
      } 
    } 
    delete div; 
    return ext; 
  }; 
  return { 
    "cssTransitions" : cssTransitions 
  }; 
}());

It’s simple and does the trick. Simply check the return of Detect.cssTransitions().

if (!Detect.cssTransitions()) {
   // Do JavaScript fallback here
}

You can also get the extension used in the current user-agent back from this method (ms, O, Moz, or Webkit).