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Message-ID: <7595870.kvP59otsHy@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <usenet@PointedEars.de>
Organization: PointedEars Software (PES)
Date: Sat, 13 Apr 2013 21:31:16 +0200
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Subject: Re: trying to call onclick with document.getElement() - document.getElement() returns null
Newsgroups: comp.lang.javascript
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Cezary Tomczyk wrote:

> W dniu 2013-04-13 13:26, Thomas 'PointedEars' Lahn pisze:
>> Cezary Tomczyk wrote:
>>> W dniu 2013-04-13 11:45, Thomas 'PointedEars' Lahn pisze:
>>>> Cezary Tomczyk wrote:
>>>>> W dniu 2013-04-13 10:29, Thomas 'PointedEars' Lahn pisze:
>>>>>> Mikael Andersson wrote:
>>>>> [...]
>>>>>>>>            if (window.XMLHttpRequest) {
>>>>>>
>>>>>> Insufficient and error-prone, see isHostMethod().
>>>>> [...]
>>>>>
>>>>> Just our of curiosity: in which environment / scenario this will not
>>>>> be properly evaluated?
>>>>
>>>> Where “XMLHttpRequest” is not a property of the object referred to by
>>>> “window”, but of another object in the scope chain.
>>>
>>> Even then isHostMethod will return true,
>>
>> No, it will return “false”.  The point is _not_ that you should call
> 
> Can you provide me an example of when this may occur?

No, you just need to read more carefully.  Hopefully a *working* 
implementation of isHostMethod() will return a false-value if the property 
in question does not exist.
 
>>    isHostMethod(window, "XMLHttpRequest")
>>
>> or
>>
>>    jsx.object.isHostMethod(jsx.global, "window", "XMLHttpRequest")
>>
>> instead – that would be equally wrong –, but that isHostMethod()
>> implements the *algorithm* to detect host methods *safely*, without
>> implicit type conversion.
> 
> I know both of methods, but sometimes simple statement "if
> (window.XMLHttpRequest)" just do the job and I never had any problems
> with that.

You were asking about possible scenarios; I have provided you with them.
You should not think that “it works” justifies approaches that are 
objectively unwise at best.  See also: Argumentum ad crumenam.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.