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Re: All ECMAScript attributes should be non-configurable

From: Brendan Eich <brendan@mozilla.org>
Date: Sat, 1 Oct 2011 01:03:09 +0200
Cc: David Bruant <david.bruant@labri.fr>, Erik Arvidsson <arv@chromium.org>, Alex Russell <slightlyoff@google.com>, "public-script-coord@w3.org" <public-script-coord@w3.org>
Message-Id: <3B984506-2D43-4E25-B4A6-B06E592D763D@mozilla.org>
To: Travis Leithead <travil@microsoft.com>
On Sep 30, 2011, at 11:18 PM, Travis Leithead wrote:

>>> +IE9 (another example using configurable properties--as accessor properties on the prototypes). We did work around the performance issue using caches, as most sites don't mess with the configurability of the properties.
>> What performance issue are you refering to? Brendan's argument was actually that this design was better in terms of performance.
> 
> The performance issue was the introduction of ECMAScript5 setters (which much be checked for anywhere in the prototype chain before assigning an own property).

The progenitor was setters and getters in SpiderMonkey, which work the same as in ES5. This spread to non-IE browsers when live.com launched in 2005 with a JS DOM emulation for non-IE browsers that assumed Firefox and SpiderMonkey, in particular __define[GS]etter__. The evolution at Apple and Opera was very fast.

/be
Received on Friday, 30 September 2011 23:03:43 UTC

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