[Fix] add awareness of Symbol.toStringTag

Fixes #20

README.md

@@ -25,6 +25,9 @@ assert.equal(isArguments([]), false);
 }())
 ```
 
+## Caveats
+If you have modified an actual `arguments` object by giving it a `Symbol.toStringTag` property, then this package will return `false`.
+
 ## Tests
 Simply clone the repo, `npm install`, and run `npm test`
 

index.js

@@ -1,8 +1,12 @@
 'use strict';
 
+var hasToStringTag = typeof Symbol === 'function' && typeof Symbol.toStringTag === 'symbol';
 var toStr = Object.prototype.toString;
 
 var isStandardArguments = function isArguments(value) {
+	if (hasToStringTag && value && Symbol.toStringTag in value) {
+		return false;
+	}
 	return toStr.call(value) === '[object Arguments]';
 };
 

test.js

@@ -2,6 +2,7 @@
 
 var test = require('tape');
 var isArguments = require('./');
+var hasToStringTag = typeof Symbol === 'function' && typeof Symbol.toStringTag === 'symbol';
 
 test('primitives', function (t) {
 	t.notOk(isArguments([]), 'array is not arguments');
@@ -26,3 +27,17 @@ test('old-style arguments object', function (t) {
 	t.ok(isLegacyArguments(fakeOldArguments), 'old-style arguments is arguments');
 	t.end();
 });
+
+test('Symbol.toStringTag', { skip: !hasToStringTag }, function (t) {
+	var obj = {};
+	obj[Symbol.toStringTag] = 'Arguments';
+	t.notOk(isArguments(obj), 'object with faked toStringTag is not arguments');
+
+	var args = (function () {
+		return arguments;
+	}());
+	args[Symbol.toStringTag] = 'Arguments';
+	t.notOk(isArguments(obj), 'real arguments with faked toStringTag is not arguments');
+
+	t.end();
+});