Inline ownEnumerableKeys into for-loop

This gives 3x performance boost in Node 0.12 and later (and 5x on Node 0.10.x)

bench.js

@@ -0,0 +1,34 @@
+var assert = require('assert');
+var lodash = require('lodash');
+var objectAssign = require('./');
+
+var source1 = {a: 1, b: 2, c: 3};
+var source2 = {c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10, k: 11, l: 12, m: 13, n: 15, o: 15, p: 16};
+
+suite('object-assign', function () {
+	bench('small', function () {
+		objectAssign({foo: 0}, {bar: 1});
+	});
+
+	bench('default options', function () {
+		objectAssign({}, {foo: 0}, {foo: 1});
+	});
+
+	bench('big', function () {
+		objectAssign({}, source1, source2);
+	});
+});
+
+suite('lodash', function () {
+	bench('small', function () {
+		lodash.assign({foo: 0}, {bar: 1});
+	});
+
+	bench('default options', function () {
+		lodash.assign({}, {foo: 0}, {foo: 1});
+	});
+
+	bench('big', function () {
+		lodash.assign({}, source1, source2);
+	});
+});

index.js

@@ -1,5 +1,5 @@
 'use strict';
-var propIsEnumerable = Object.prototype.propertyIsEnumerable;
+var hasOwnProperty = Object.prototype.hasOwnProperty;
 
 function ToObject(val) {
 	if (val == null) {
@@ -9,29 +9,26 @@ function ToObject(val) {
 	return Object(val);
 }
 
-function ownEnumerableKeys(obj) {
-	var keys = Object.getOwnPropertyNames(obj);
-
-	if (Object.getOwnPropertySymbols) {
-		keys = keys.concat(Object.getOwnPropertySymbols(obj));
-	}
-
-	return keys.filter(function (key) {
-		return propIsEnumerable.call(obj, key);
-	});
-}
-
 module.exports = Object.assign || function (target, source) {
 	var from;
 	var keys;
 	var to = ToObject(target);
+	var symbols;
 
 	for (var s = 1; s < arguments.length; s++) {
-		from = arguments[s];
-		keys = ownEnumerableKeys(Object(from));
+		from = Object(arguments[s]);
+
+		for (var key in from) {
+			if (hasOwnProperty.call(from, key)) {
+				to[key] = from[key];
+			}
+		}
 
-		for (var i = 0; i < keys.length; i++) {
-			to[keys[i]] = from[keys[i]];
+		if (Object.getOwnPropertySymbols) {
+			symbols = Object.getOwnPropertySymbols(from);
+			for (var i = 0; i < symbols.length; i++) {
+				to[symbols[i]] = from[symbols[i]];
+			}
 		}
 	}
 

package.json

@@ -13,7 +13,8 @@
     "node": ">=0.10.0"
   },
   "scripts": {
-    "test": "mocha"
+    "test": "mocha",
+    "bench": "matcha bench.js"
   },
   "files": [
     "index.js"
@@ -33,6 +34,8 @@
     "browser"
   ],
   "devDependencies": {
+    "lodash": "^3.10.1",
+    "matcha": "^0.6.0",
     "mocha": "*"
   }
 }