So siehts ganz gut aus !

node_modules/es5-ext/object/ensure-plain-function.js

@@ -0,0 +1,11 @@
+"use strict";
+
+var safeToString    = require("../safe-to-string")
+  , isPlainFunction = require("./is-plain-function");
+
+module.exports = function (value) {
+	if (!isPlainFunction(value)) {
+		throw new TypeError(safeToString(value) + " is not a plain function");
+	}
+	return value;
+};