Using the `in` operator with host objects
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From: Thomas 'PointedEars' Lahn on 18 May 2010 07:54 Garrett Smith wrote: > A bit of advice here regarding the `in` operator [with host objects]. > In a nutshell: Avoid doing that. > [...] > It is generally safer to use the typeof operator and compare the result > against undefined. I believe I have been telling that for years. Well, better late than never. The "catchall" probably makes it to a footnote in the ECMAScript Support Matrix, though. PointedEars -- Anyone who slaps a 'this page is best viewed with Browser X' label on a Web page appears to be yearning for the bad old days, before the Web, when you had very little chance of reading a document written on another computer, another word processor, or another network. -- Tim Berners-Lee
From: Garrett Smith on 18 May 2010 14:29
David Mark wrote: > Garrett Smith wrote: >> David Mark wrote: >>> Garrett Smith wrote: [...] >> You did not explain the reasons for why it doesn't work. My explanation >> explains how catchalls work shows where they affect the `in` operator. > > It doesn't matter if I explained them or not. Like the "revelation" > about properties of ActiveX objects, and various other things over the > years, I ultimately turned out to be right (and you turned out to be > wrong). That's my point. ;) Would a catchall be implemented with a method lookup, as: if("createElement" in document) ; An implementation wouldn't have a good reason to use a catchall for that. A catchall would be used to try to get a value from an object, such as with the indexed getters or name getters from collections such as navigator.plugins. -- Garrett comp.lang.javascript FAQ: http://jibbering.com/faq/ |