Prevent v8 deopt with a few simple tweaks.

Benchmark script shows a roughly ~40% improvement in model creation.

ampersand-state.js

@@ -1,3 +1,4 @@
+'use strict';
 /*$AMPERSAND_VERSION*/
 var uniqueId = require('lodash.uniqueid');
 var assign = require('lodash.assign');
@@ -625,16 +626,16 @@ var dataTypes = {
             if (newVal == null) {
                 newType = typeof null;
             } else if (!isDate(newVal)) {
-                try {
-                    var dateVal = new Date(newVal).valueOf();
-                    if (isNaN(dateVal)) {
-                        // If the newVal cant be parsed, then try parseInt first
-                        dateVal = new Date(parseInt(newVal, 10)).valueOf();
-                        if (isNaN(dateVal)) throw TypeError;
-                    }
-                    newVal = dateVal;
-                    newType = 'date';
-                } catch (e) {
+                var err = null;
+                var dateVal = new Date(newVal).valueOf();
+                if (isNaN(dateVal)) {
+                    // If the newVal cant be parsed, then try parseInt first
+                    dateVal = new Date(parseInt(newVal, 10)).valueOf();
+                    if (isNaN(dateVal)) err = true;
+                }
+                newVal = dateVal;
+                newType = 'date';
+                if (err) {
                     newType = typeof newVal;
                 }
             } else {
@@ -725,9 +726,9 @@ var dataTypes = {
 // the extend method used to extend prototypes, maintain inheritance chains for instanceof
 // and allow for additions to the model definitions.
 function extend(protoProps) {
+    /*jshint validthis:true*/
     var parent = this;
     var child;
-    var args = [].slice.call(arguments);
 
     // The constructor function for the new subclass is either defined by you
     // (the "constructor" property in your `extend` definition), or defaulted
@@ -762,7 +763,8 @@ function extend(protoProps) {
         var omitFromExtend = [
             'dataTypes', 'props', 'session', 'derived', 'collections', 'children'
         ];
-        args.forEach(function processArg(def) {
+        for(var i = 0; i < arguments.length; i++) {
+            var def = arguments[i];
             if (def.dataTypes) {
                 forEach(def.dataTypes, function (def, name) {
                     child.prototype._dataTypes[name] = def;
@@ -794,7 +796,7 @@ function extend(protoProps) {
                 });
             }
             assign(child.prototype, omit(def, omitFromExtend));
-        });
+        }
     }
 
     // Set a convenience property in case the parent's prototype is needed

benchmark/massCreate.js

@@ -0,0 +1,54 @@
+var State = require('../ampersand-state');
+
+function createModel() {
+  var aModel = State.extend({
+    derived: {
+      foo: {
+        deps: ['a', 'b'],
+        fn: function derived () {
+          return this.a + this.b;
+        }
+      }
+    }
+  });
+  return aModel;
+}
+
+//Function that contains the pattern to be inspected
+var aModel = createModel();
+function benchFn() {
+  return new aModel({a: 1, b: 2}).foo;
+}
+
+function printStatus(fn) {
+    switch(%GetOptimizationStatus(fn)) {
+        case 1: console.log("Function is optimized"); break;
+        case 2: console.log("Function is not optimized"); break;
+        case 3: console.log("Function is always optimized"); break;
+        case 4: console.log("Function is never optimized"); break;
+        case 6: console.log("Function is maybe deoptimized"); break;
+    }
+}
+
+//Fill type-info
+benchFn();
+// 2 calls are needed to go from uninitialized -> pre-monomorphic -> monomorphic
+benchFn();
+benchFn();
+benchFn();
+benchFn();
+benchFn();
+
+%OptimizeFunctionOnNextCall(benchFn);
+//The next call
+benchFn();
+
+//Check
+printStatus(benchFn);
+
+
+console.time('createAModel');
+for (var i = 0; i < 10000;i++) {
+  benchFn();
+}
+console.timeEnd('createAModel');

package.json

@@ -70,7 +70,8 @@
     "test": "browserify test/index.js | tape-run | tap-spec",
     "validate": "npm ls",
     "start": "run-browser test/index.js",
-    "lint": "jshint .",
+    "lint": "jshint --exclude benchmark/ .",
+    "benchmark": "node --allow-natives-syntax benchmark/massCreate.js",
     "preversion": "git checkout master && git pull && npm ls",
     "publish-patch": "npm run preversion && npm version patch && git push origin master --tags && npm publish",
     "publish-minor": "npm run preversion && npm version minor && git push origin master --tags && npm publish",