feat: support propertyNames option in Object.copy

object/copy.js

@@ -1,10 +1,21 @@
-'use strict';
+"use strict";
 
-var assign = require('./assign')
-  , value  = require('./valid-value');
+var aFrom                = require("../array/from")
+  , assign               = require("./assign")
+  , value                = require("./valid-value")
+  , propertyIsEnumerable = Object.prototype.propertyIsEnumerable;
 
-module.exports = function (obj) {
-	var copy = Object(value(obj));
-	if (copy !== obj) return copy;
-	return assign({}, obj);
+module.exports = function(obj /*, propertyNames*/) {
+	var copy = Object(value(obj)), propertyNames = arguments[1];
+	if (copy !== obj && !propertyNames) return copy;
+	var result = {};
+	if (propertyNames) {
+		aFrom(propertyNames, function(propertyName) {
+			if (propertyIsEnumerable.call(obj, propertyName))
+				result[propertyName] = obj[propertyName];
+		});
+	} else {
+		assign(result, obj);
+	}
+	return result;
 };

test/object/copy.js

@@ -1,19 +1,27 @@
-'use strict';
+"use strict";
 
 var stringify = JSON.stringify;
 
-module.exports = function (t, a) {
-	var o = { 1: 'raz', 2: 'dwa', 3: 'trzy' }
-	  , no = t(o);
+module.exports = function(t, a) {
+	var o = { 1: "raz", 2: "dwa", 3: "trzy" }, no = t(o);
 
 	a.not(no, o, "Return different object");
 	a(stringify(no), stringify(o), "Match properties and values");
 
-	o = { foo: 'bar', raz: { dwa: 'dwa',
-		trzy: { cztery: 'pięć', 'sześć': 'siedem' }, osiem: {},
-		'dziewięć': function () { } }, 'dziesięć': 10 };
+	o = {
+		foo: "bar",
+		raz: {
+			dwa: "dwa",
+			trzy: { cztery: "pięć", sześć: "siedem" },
+			osiem: {},
+			dziewięć: function() {}
+		},
+		dziesięć: 10
+	};
 	o.raz.rec = o;
 
 	no = t(o);
 	a(o.raz, no.raz, "Shallow");
+
+	a.deep(t(o, ["foo"]), { foo: "bar" });
 };