On Oct 29, 2014, at 4:03 PM, Boris Zbarsky <[email protected]> wrote:
> On 10/29/14, 2:55 PM, Allen Wirfs-Brock wrote: >> ES since forever have made special provisions about when shadowing of such >> properties are allowed. Both global var and function declarations reused >> any global object existing property for the declared name, except that >> function declarations refused to change the value of non-configurable >> readonly properties. > > "var undefined = 5" doesn't change the value of undefined evaluated in global > scope, right? Prior to the ES5 spec. it actually did, as undefined was writable. > >> If browsers use the same semantic mechanisms a libraries (or the >> implementation level equivalent) then they will behave identically. > > What browsers are doing here is defining non-configurable accessor (or > readonly value, for some browsers) properties on the global. As far as I can > tell, "var" and "function" can't mess with such properties today. It’s a bit more complicated than that. See https://bugs.ecmascript.org/show_bug.cgi?id=78 which is a bug against ES5.1 is addressed in the ES6 spec. Also see the reference firefox bug. I suspect it will jog you memory. Allen
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