Merge pull request #32 from spicyj/bugtest

Add feature test against buggy V8 versions

index.js

@@ -11,7 +11,51 @@ function toObject(val) {
 	return Object(val);
 }
 
-module.exports = Object.assign || function (target, source) {
+function shouldUseNative() {
+	try {
+		if (!Object.assign) {
+			return false;
+		}
+
+		// Detect buggy property enumeration order in older V8 versions.
+
+		// https://bugs.chromium.org/p/v8/issues/detail?id=4118
+		var test1 = new String('abc');  // eslint-disable-line
+		test1[5] = 'de';
+		if (Object.getOwnPropertyNames(test1)[0] === '5') {
+			return false;
+		}
+
+		// https://bugs.chromium.org/p/v8/issues/detail?id=3056
+		var test2 = {};
+		for (var i = 0; i < 10; i++) {
+			test2['_' + String.fromCharCode(i)] = i;
+		}
+		var order2 = Object.getOwnPropertyNames(test2).map(function (n) {
+			return test2[n];
+		});
+		if (order2.join('') !== '0123456789') {
+			return false;
+		}
+
+		// https://bugs.chromium.org/p/v8/issues/detail?id=3056
+		var test3 = {};
+		'abcdefghijklmnopqrst'.split('').forEach(function (letter) {
+			test3[letter] = letter;
+		});
+		if (Object.keys(Object.assign({}, test3)).join('') !==
+				'abcdefghijklmnopqrst') {
+			return false;
+		}
+
+		return true;
+	} catch (e) {
+		// We don't expect any of the above to throw, but better to be safe.
+		return false;
+	}
+}
+
+module.exports = shouldUseNative() ? Object.assign : function (target, source) {
 	var from;
 	var to = toObject(target);
 	var symbols;