browserVersionOf.js

function browserVersionOf(unprefixedName, parentObject) {
  // parentObject is optional and usually omitted, set it to window if it's not specified.
  parentObject = parentObject || window;
  var baseName = unprefixedName.charAt(0).toUpperCase() + unprefixedName.substring(1);
  var i = 0, variants = [unprefixedName, 'webkit', 'moz', 'ms', 'o'];
  var fullName = variants[0];
  do {
    if (typeof parentObject[fullName] == 'function') {
      return parentObject[fullName];
    }
    fullName = variants[++i] + baseName;
  } while (variants[i]);
  throw "Browser lacks support for " + unprefixedName;
}