Cache property value.

underscore.js

@@ -876,7 +876,8 @@
   // Get a value from an object as a property or as a function.
   _.getValue = function(object, prop) {
     if (object == null) return null;
-    return _.isFunction(object[prop]) ? object[prop]() : object[prop];
+    var value = object[prop];
+    return _.isFunction(value) ? value() : value;
   };
 
   // Add your own custom functions to the Underscore object, ensuring that