code: function(func, context, argCount) {
                  if (context === void 0) return func;
                  switch (argCount == null ? 3 : argCount) {
                    case 1: return function(value) {
                      return func.call(context, value);
                    };
                    case 2: return function(value, other) {
                      return func.call(context, value, other);
                    };
                    case 3: return function(value, index, collection) {
                      return func.call(context, value, index, collection);
                    };
                    case 4: return function(accumulator, value, index, collection) {
                      return func.call(context, accumulator, value, index, collection);
                    };
                  }
                  return function() {
                    return func.apply(context, arguments);
                  };
                }
docs: Internal function that returns an efficient (for current engines) version of the passed-in callback, to be repeatedly applied in other Underscore functions.