detect.js

define(['implementations'], function (impls) {
  var map = {},
      isArray = function (it) {
        return {}.toString.call(it) == '[object Array]';
      },
      isAvailable = function (impl, name) {
        var isFunction = typeof impl.isAvailable === 'function';
        return (isFunction && impl.isAvailable(name)) || (!isFunction && impl.isAvailable);
      };

  for (var name in impls) {
    var featureInfo = impls[name],
        mapItem = map[name] = {};

    if (isArray(featureInfo)) {
      for (var i = 0, m = featureInfo.length; i < m; i++) {
        if (isAvailable(featureInfo[i], name)) {
          mapItem.implementedBy = featureInfo[i].implementation;
          mapItem.testSource = featureInfo[i].isAvailable.toString();
          break;
        }
      }
    } else {
      mapItem.implementedBy = featureInfo;
    }
  }

  return map;
});