a very simple and cross platform way to grab some experimental function

find-or-fallback.js

function findOrFallback(where, what, fallback) {
  for(var
    vendors = ['', 'webkit', 'moz', 'ms', 'o'],
    first = what.charAt(0),
    others = first.toUpperCase(),
    suffix = what.slice(1),
    i = 0, length = vendors.length,
    current;
    i < length; i++
  ) {
    current = where[vendors[i] + (i ? others : first) + suffix];
    if (current) return current;
  }
  return fallback;
}

// example
var requestAnimationFrame = findOrFallback(
  window, 'requestAnimationFrame', function(fn){
    return setTimeout(fn, 1000 / 60);
  }
);

If you are looking for a more complete features finder, check experimental out