diff --git a/knockout.mapping.js b/knockout.mapping.js
index 2ac4a3d..ed30f75 100644
--- a/knockout.mapping.js
+++ b/knockout.mapping.js
@@ -28,27 +28,27 @@
 		observe: []
 	};
 	var defaultOptions = _defaultOptions;
-	
+
 	function unionArrays() {
 		var args = arguments,
 		l = args.length,
 		obj = {},
 		res = [],
 		i, j, k;
-		
+
 		while (l--) {
 			k = args[l];
 			i = k.length;
-			
+
 			while (i--) {
 				j = k[i];
 				if (!obj[j]) {
 					obj[j] = 1;
 					res.push(j);
 				}
-			}	
+			}
 		}
-		
+
 		return res;
 	}
 
@@ -126,7 +126,7 @@
 					var DO = dependentObservables.pop();
 					if (DO) {
 						DO();
-						
+
 						// Move this magic property to the underlying dependent observable
 						DO.__DO["throttleEvaluation"] = DO["throttleEvaluation"];
 					}
@@ -197,11 +197,14 @@
 	};
 
 	exports.getType = function(x) {
-		if ((x) && (typeof (x) === "object")) {
-			if (x.constructor === Date) return "date";
-			if (x.constructor === Array) return "array";
+		switch (Object.prototype.toString.call(x)) {
+			case "[object Date]":
+				return "date";
+			case "[object Array]":
+				return "array";
+			default:
+				return typeof x;
 		}
-		return typeof x;
 	}
 
 	function fillOptions(rawOptions, otherOptions) {
@@ -210,12 +213,12 @@
 		// Move recognized root-level properties into a root namespace
 		for (var i = recognizedRootProperties.length - 1; i >= 0; i--) {
 			var property = recognizedRootProperties[i];
-			
+
 			// Carry on, unless this property is present
 			if (!options[property]) continue;
-			
+
 			// Move the property into the root namespace
-			if (!(options[""] instanceof Object)) options[""] = {};
+			if (!(exports.getType(options[""]) === "object")) options[""] = {};
 			options[""][property] = options[property];
 			delete options[property];
 		}
@@ -290,7 +293,7 @@
 				wrapped.__DO = DO;
 				return wrapped;
 			};
-			
+
 			options.deferEvaluation = true; // will either set for just options, or both read/options.
 			var realDependentObservable = new realKoDependentObservable(read, owner, options);
 
@@ -326,13 +329,14 @@
 		};
 
 		var hasCreateCallback = function () {
-			return options[parentName] && options[parentName].create instanceof Function;
+			return options[parentName] &&
+						 exports.getType(options[parentName].create) === "function";
 		};
 
 		var createCallback = function (data) {
 			return withProxyDependentObservable(dependentObservables, function () {
-				
-				if (ko.utils.unwrapObservable(parent) instanceof Array) {
+
+				if (exports.getType(ko.utils.unwrapObservable(parent)) === "array") {
 					return options[parentName].create({
 						data: data || callbackParams.data,
 						parent: callbackParams.parent,
@@ -343,12 +347,13 @@
 						data: data || callbackParams.data,
 						parent: callbackParams.parent
 					});
-				}				
+				}
 			});
 		};
 
 		var hasUpdateCallback = function () {
-			return options[parentName] && options[parentName].update instanceof Function;
+			return options[parentName] &&
+						 exports.getType(options[parentName].update) === "function";
 		};
 
 		var updateCallback = function (obj, data) {
@@ -401,7 +406,7 @@
 						}
 					} else {
 						var hasCreateOrUpdateCallback = hasCreateCallback() || hasUpdateCallback();
-						
+
 						if (hasCreateCallback()) {
 							mappedRootObject = createCallback();
 						} else {
@@ -411,7 +416,7 @@
 						if (hasUpdateCallback()) {
 							mappedRootObject(updateCallback(mappedRootObject));
 						}
-						
+
 						if (hasCreateOrUpdateCallback) return mappedRootObject;
 					}
 				}
@@ -462,20 +467,20 @@
 						options.copiedProperties[fullPropertyName] = true;
 						return;
 					}
-					
+
 					// In case we are adding an already mapped property, fill it with the previously mapped property value to prevent recursion.
 					// If this is a property that was generated by fromJS, we should use the options specified there
 					var prevMappedProperty = visitedObjects.get(rootObject[indexer]);
 					var retval = updateViewModel(mappedRootObject[indexer], rootObject[indexer], options, indexer, mappedRootObject, fullPropertyName, mappedRootObject);
 					var value = prevMappedProperty || retval;
-					
+
 					if(options.observe.length > 0 && ko.utils.arrayIndexOf(options.observe, fullPropertyName) == -1)
 					{
 						mappedRootObject[indexer] = ko.utils.unwrapObservable(value);
 						options.copiedProperties[fullPropertyName] = true;
 						return;
 					}
-					
+
 					if (ko.isWriteableObservable(mappedRootObject[indexer])) {
 						value = ko.utils.unwrapObservable(value);
 						if (mappedRootObject[indexer]() !== value) {
@@ -572,7 +577,7 @@
 			var editScript = ko.utils.compareArrays(currentArrayKeys, newArrayKeys);
 
 			var ignoreIndexOf = {};
-			
+
 			var i, j;
 
 			var unwrappedRootObject = ko.utils.unwrapObservable(rootObject);
@@ -580,7 +585,7 @@
 			var optimizedKeys = true;
 			for (i = 0, j = unwrappedRootObject.length; i < j; i++) {
 				var key = keyCallback(unwrappedRootObject[i]);
-				if (key === undefined || key instanceof Object) {
+				if (key === undefined || exports.getType(key) === "object") {
 					optimizedKeys = false;
 					break;
 				}
@@ -602,13 +607,13 @@
 					}
 
 					var index = ignorableIndexOf(ko.utils.unwrapObservable(rootObject), item, ignoreIndexOf);
-					
+
 					if (mappedItem === emptyReturn) {
 						passedOver++;
 					} else {
 						newContents[index - passedOver] = mappedItem;
 					}
-						
+
 					ignoreIndexOf[index] = true;
 					break;
 				case "retained":
@@ -785,10 +790,10 @@
 			return value;
 		};
 	};
-	
+
 	function objectLookup() {
 		var buckets = {};
-		
+
 		var findBucket = function(key) {
 			var bucketKey;
 			try {
@@ -805,7 +810,7 @@
 			}
 			return bucket;
 		};
-		
+
 		this.save = function (key, value) {
 			findBucket(key).save(key, value);
 		};