So siehts ganz gut aus !

node_modules/es5-ext/array/#/last-index.js

@@ -0,0 +1,15 @@
+"use strict";
+
+var toPosInt          = require("../../number/to-pos-integer")
+  , value             = require("../../object/valid-value")
+  , objHasOwnProperty = Object.prototype.hasOwnProperty;
+
+module.exports = function () {
+	var i, length;
+	if (!(length = toPosInt(value(this).length))) return null;
+	i = length - 1;
+	while (!objHasOwnProperty.call(this, i)) {
+		if (--i === -1) return null;
+	}
+	return i;
+};