`({[Symbol.toStringTag]: 'String'})` could be identified as string as well, use the legacy method. ES6 guarantees that legacy code will work, but it does not ensure that legacy code could work well with new codes that intended to create a fake string.

Subject: Re: @@toStringTag spoofing for null and undefined
From: claude.pache at gmail.com
Date: Tue, 10 Feb 2015 09:54:03 +0100
CC: es-discuss at mozilla.org
To: nbdd0121 at hotmail.com

Changing `String.prototype` from String to non-String is indeed a risk by itself. But the issue I was mentioning is independent of that, namely that an unknown object would be misidentified as String and would throw on methods that work only on Strings, e.g.: `if (getType(obj) == "String") { return obj.toUpperCase() }`, where `getType()` is based on `O.p.toString`.
 		 	   		  
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`({[Symbol.toStringTag]: 'String'})` could be identified as string as well, use the legacy method. ES6 guarantees that legacy code will work, but it does not ensure that legacy code could work well with new codes that intended to create a fake string.