Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.javascript > #19245 > unrolled thread

trying to call onclick with document.getElement() - document.getElement() returns null

Back to article view | Back to comp.lang.javascript

Contents

  trying to call onclick with document.getElement() - document.getElement() returns null jorythompson@gmail.com - 2013-04-12 10:45 -0700
    Re: trying to call onclick with document.getElement() - document.getElement() returns null Jordan Thompson <jorythompson@gmail.com> - 2013-04-12 11:01 -0700
    Re: trying to call onclick with document.getElement() - document.getElement() returns null Mikael Andersson <qubex2@gmail.com> - 2013-04-12 21:31 +0200
      Re: trying to call onclick with document.getElement() - document.getElement() returns null Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-04-13 10:29 +0200
        Re: trying to call onclick with document.getElement() - document.getElement() returns null Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2013-04-13 11:10 +0200
          Re: trying to call onclick with document.getElement() - document.getElement() returns null Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-04-13 11:45 +0200
            Re: trying to call onclick with document.getElement() - document.getElement() returns null Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2013-04-13 13:04 +0200
              Re: trying to call onclick with document.getElement() - document.getElement() returns null Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-04-13 13:26 +0200
                Re: trying to call onclick with document.getElement() - document.getElement() returns null Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2013-04-13 21:12 +0200
                  Re: trying to call onclick with document.getElement() - document.getElement() returns null Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-04-13 21:31 +0200
                    Re: trying to call onclick with document.getElement() - document.getElement() returns null Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2013-04-16 20:01 +0200
                      Re: trying to call onclick with document.getElement() - document.getElement() returns null Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-04-16 23:13 +0200
        Re: trying to call onclick with document.getElement() - document.getElement() returns null Mikael Andersson <qubex2@gmail.com> - 2013-04-13 18:35 +0200

#19245 — trying to call onclick with document.getElement() - document.getElement() returns null

Hi all,
I am sorry if this is in the wrong group, but it (mostly) involves javascript, so I thought appropriate to post here (even though there is some php.)  

When I run this, the popup shows null,null,null (indicating the document.getElementById() calls are not finding the appropriate ids.)  I realize I will need to call .value on these, but will do so after I get around the null returns.

Any help here would be most welcomed!


Here is my code (note the only thing in db.php is setting up the database connection with username, password, etc.  This works fine in other pages.

*****************************************************************************
options.php:
*****************************************************************************
<?php
  require($_SERVER['DOCUMENT_ROOT'].'/../cgi-bin2/db.php');
  function showCitiesCombo($name) {
    $result = mysql_query("SELECT distinct city FROM Lot ORDER BY city");
    echo 'Select a City:<br>';
    echo '<select name="' . $name . '" multiple>';
      echo '<form>';
        while($row = mysql_fetch_array($result)) {
          if ($row['city'] != "") {
            echo '<option value="' . $row['city'] .'">' . $row['city'] . '</option>';
          }
        }
		  echo '</select>';
    echo '</form>';
  }

  function showStatesCombo($name) {
    $result = mysql_query("SELECT distinct usState FROM Lot ORDER BY usState");
    echo 'Select a State:<br>';
    echo '<select name="' . $name . '">';
      echo '<form>';
        while($row = mysql_fetch_array($result)) {
          echo '<option value="' . $row['usState'] .'">' . $row['usState'] . '</option>';
        }
      echo '</select>';
    echo '</form>';
  }
?>



*****************************************************************************
index.php:
*****************************************************************************
<!DOCTYPE HTML>
  <?php
    session_start();
    require($_SERVER['DOCUMENT_ROOT'].'/../cgi-bin2/options.php');
  ?>
  
  <html>
    <body>
      <form>
        <?php
          showStatesCombo('cities');
          showCitiesCombo('states');
          echo "<br>";
        ?>
        Street: <input type="text" name="street"><br>
        <input name="buttonExecute" 
        onclick="searchForLots()"
        type="button" value="Search" />
      </form>
      <br>
      <div id="tableTarget"><b></b></div>
    </body>

    <script>
      function searchForLots() {
        street = document.getElementById('street');
        city = document.getElementById('cities');
        state = document.getElementById('state');
        
        if (window.XMLHttpRequest) {
          // code for IE7+, Firefox, Chrome, Opera, Safari
          xmlhttp=new XMLHttpRequest();
        } else {
          // code for IE6, IE5
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
        
        xmlhttp.onreadystatechange=function() {
          if (xmlhttp.readyState==4 && xmlhttp.status==200) {
            document.getElementById("tableTarget").innerHTML=xmlhttp.responseText;
          }
        }

        alert(street + ", " + city +", " + state);
        xmlhttp.open("GET","searchForLots.php?city="+city+"&state="+state+"&street="+street, true);
        xmlhttp.send();
      }
    </script>
</html>

[toc] | [next] | [standalone]

#19246

duh... It seems that the control uses id= and not name= to identify itself.

On Friday, April 12, 2013 1:45:03 PM UTC-4, Jordan Thompson wrote:
> Hi all,
> 
> I am sorry if this is in the wrong group, but it (mostly) involves javascript, so I thought appropriate to post here (even though there is some php.)  
> 
> 
> 
> When I run this, the popup shows null,null,null (indicating the document.getElementById() calls are not finding the appropriate ids.)  I realize I will need to call .value on these, but will do so after I get around the null returns.
> 
> 
> 
> Any help here would be most welcomed!
> 
> 
> 
> 
> 
> Here is my code (note the only thing in db.php is setting up the database connection with username, password, etc.  This works fine in other pages.
> 
> 
> 
> *****************************************************************************
> 
> options.php:
> 
> *****************************************************************************
> 
> <?php
> 
>   require($_SERVER['DOCUMENT_ROOT'].'/../cgi-bin2/db.php');
> 
>   function showCitiesCombo($name) {
> 
>     $result = mysql_query("SELECT distinct city FROM Lot ORDER BY city");
> 
>     echo 'Select a City:<br>';
> 
>     echo '<select name="' . $name . '" multiple>';
> 
>       echo '<form>';
> 
>         while($row = mysql_fetch_array($result)) {
> 
>           if ($row['city'] != "") {
> 
>             echo '<option value="' . $row['city'] .'">' . $row['city'] . '</option>';
> 
>           }
> 
>         }
> 
> 		  echo '</select>';
> 
>     echo '</form>';
> 
>   }
> 
> 
> 
>   function showStatesCombo($name) {
> 
>     $result = mysql_query("SELECT distinct usState FROM Lot ORDER BY usState");
> 
>     echo 'Select a State:<br>';
> 
>     echo '<select name="' . $name . '">';
> 
>       echo '<form>';
> 
>         while($row = mysql_fetch_array($result)) {
> 
>           echo '<option value="' . $row['usState'] .'">' . $row['usState'] . '</option>';
> 
>         }
> 
>       echo '</select>';
> 
>     echo '</form>';
> 
>   }
> 
> ?>
> 
> 
> 
> 
> 
> 
> 
> *****************************************************************************
> 
> index.php:
> 
> *****************************************************************************
> 
> <!DOCTYPE HTML>
> 
>   <?php
> 
>     session_start();
> 
>     require($_SERVER['DOCUMENT_ROOT'].'/../cgi-bin2/options.php');
> 
>   ?>
> 
>   
> 
>   <html>
> 
>     <body>
> 
>       <form>
> 
>         <?php
> 
>           showStatesCombo('cities');
> 
>           showCitiesCombo('states');
> 
>           echo "<br>";
> 
>         ?>
> 
>         Street: <input type="text" name="street"><br>
> 
>         <input name="buttonExecute" 
> 
>         onclick="searchForLots()"
> 
>         type="button" value="Search" />
> 
>       </form>
> 
>       <br>
> 
>       <div id="tableTarget"><b></b></div>
> 
>     </body>
> 
> 
> 
>     <script>
> 
>       function searchForLots() {
> 
>         street = document.getElementById('street');
> 
>         city = document.getElementById('cities');
> 
>         state = document.getElementById('state');
> 
>         
> 
>         if (window.XMLHttpRequest) {
> 
>           // code for IE7+, Firefox, Chrome, Opera, Safari
> 
>           xmlhttp=new XMLHttpRequest();
> 
>         } else {
> 
>           // code for IE6, IE5
> 
>           xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
> 
>         }
> 
>         
> 
>         xmlhttp.onreadystatechange=function() {
> 
>           if (xmlhttp.readyState==4 && xmlhttp.status==200) {
> 
>             document.getElementById("tableTarget").innerHTML=xmlhttp.responseText;
> 
>           }
> 
>         }
> 
> 
> 
>         alert(street + ", " + city +", " + state);
> 
>         xmlhttp.open("GET","searchForLots.php?city="+city+"&state="+state+"&street="+street, true);
> 
>         xmlhttp.send();
> 
>       }
> 
>     </script>
> 
> </html>

[toc] | [prev] | [next] | [standalone]

#19248

jorythompson@gmail.com writes:

[snip]
> *****************************************************************************
> <?php
>   require($_SERVER['DOCUMENT_ROOT'].'/../cgi-bin2/db.php');
>   function showCitiesCombo($name) {
>     $result = mysql_query("SELECT distinct city FROM Lot ORDER BY city");
>     echo 'Select a City:<br>';
>     echo '<select name="' . $name . '" multiple>';
>       echo '<form>';
>         while($row = mysql_fetch_array($result)) {
>           if ($row['city'] != "") {

[snip]
>     <script>
>       function searchForLots() {
>         street = document.getElementById('street');
>         city = document.getElementById('cities');
>         state = document.getElementById('state');
>         
>         if (window.XMLHttpRequest) {
>           // code for IE7+, Firefox, Chrome, Opera, Safari


Hi,

You should either use document.getElementsByName('street'), which
returns an array. Or change the select to: (you can in php write)

echo "<select name='$name' id='$name'>";
                           ^^
easier to read and understand. When using " double quotes you can have
php variables inside.

Yours,
QubeX2

[toc] | [prev] | [next] | [standalone]

#19250

Mikael Andersson wrote:

> jorythompson@gmail.com writes:
> 
> [snip]
>> 
*****************************************************************************
>> <?php
>>   require($_SERVER['DOCUMENT_ROOT'].'/../cgi-bin2/db.php');

Use “require_once”, remove the parentheses (it is not a function call), and 
see <http://php.net/include_path> and <http://php.net/autoload> for how to 
avoid this partially or altogether.

>>   function showCitiesCombo($name) {
>>     $result = mysql_query("SELECT distinct city FROM Lot ORDER BY city");

Never do it that way, see the warning in <http://php.net/mysql_query>.

>>     echo 'Select a City:<br>';
>>     echo '<select name="' . $name . '" multiple>';
>>       echo '<form>';

Never do it that way; write templates that you include, as a first step to 
separate presentation from business logic.  See also: MVC.

>>         while($row = mysql_fetch_array($result)) {

Make it clear that you are evaluating the right-hand side of the assignment:

  while (($row = mysql_fetch_array($result))) {

But see above.

>>           if ($row['city'] != "") {
> 
> [snip]
>>     <script>
>>       function searchForLots() {
>>         street = document.getElementById('street');
>>         city = document.getElementById('cities');
>>         state = document.getElementById('state');

You have neglected to declare your identifiers as local variables.  So by 
assignment they become names of properties of the Global Object, if that.
Instead:

  var street = …
  …

>>         if (window.XMLHttpRequest) {

Insufficient and error-prone, see isHostMethod().

>>           // code for IE7+, Firefox, Chrome, Opera, Safari

Learn to think in terms of layout engines and object models, not browsers.

<http://www.w3.org/TR/XMLHttpRequest/>

> You should either use document.getElementsByName('street'), which
> returns an array.

No, it does not.  It returns a reference to an object that implements the 
NodeList interface.  In some DOM implementations (like the Gecko DOM), that 
object also implements the HTMLCollection interface.

<http://www.w3.org/TR/2012/CR-html5-20121217/dom.html#dom-document-
getelementsbyname>

> Or change the select to: (you can in php write)
> 
> echo "<select name='$name' id='$name'>";
>                            ^^
> easier to read and understand. When using " double quotes you can have
> php variables inside.

  <select name="<?php echo ($name = htmlspecialchars($name, …)); ?>" 
          id="<?php echo $name; ?>">

or (PHP 5.4+)

  <select name="<?= ($name = htmlspecialchars($name, …)); ?>" 
          id="<?= $name; ?>">

is recommended instead.  Works better with templates, too.  However, a case 
could be made for DRY, so that

  <select <?php
    echo sprintf('name="%s" id="%*1$s"', htmlspecialchars($name, …));
  ?>>

becomes an option.

<http://php.net/manual/en/tutorial.firstpage.php>
<http://php.net/htmlspecialchars>
<http://php.net/manual/en/migration54.new-features.php>
<http://php.net/sprintf>

Note that IDs must be unique in an element's home subtree; names for 
controls do not need to.

<http://www.w3.org/TR/2012/CR-html5-20121217/dom.html#the-id-attribute>
<http://www.w3.org/TR/2012/CR-html5-20121217/forms.html#attr-fe-name>

-- 
PointedEars

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

[toc] | [prev] | [next] | [standalone]

#19252

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?

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/

[toc] | [prev] | [next] | [standalone]

#19254

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.

Where the host object referred to by “window.XMLHttpRequest” does not take 
kindly (read: throws unrecoverable exceptions) on being subjected to a
type-converting test.

See previous discussions that lead to isHostMethod().

-- 
PointedEars

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

[toc] | [prev] | [next] | [standalone]

#19255

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, which is not really what is 
expected. By testing window.XMLHttpRequest I assume that there is really 
"XMLHttpRequest" object. So, changing this is asking for trouble.

> Where the host object referred to by “window.XMLHttpRequest” does not take
> kindly (read: throws unrecoverable exceptions) on being subjected to a
> type-converting test.

You referring to 'unknown' type returned by typeof operator in Internet 
Explorer, right?

> See previous discussions that lead to isHostMethod().

Yes, I know isHostMethod, but regarding "if (window.XMLHttpRequest)" I 
had no problems with this feature detection. However, I know that 
testing by typeof some of ActiveX objects may return 'unknown' type.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/

[toc] | [prev] | [next] | [standalone]

#19257

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
  
  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.

> […]
> By testing window.XMLHttpRequest I assume that there is really
> "XMLHttpRequest" object.

No, you are assuming that there is an object in the scope chain that has a 
“window” property, which is storing a reference to an object that has an 
“XMLHttpRequest” property that is storing a reference to an object that, 
when [[Constructed]], returns a reference to an object that implements the 
“XMLHttpRequest” interface.

> So, changing this is asking for trouble.
 
Doing it like this is asking for trouble, because “With host objects, all 
bets are off.“ (Lasse Reichstein Nielsen in cljs)

>> Where the host object referred to by “window.XMLHttpRequest” does not
>> take kindly (read: throws unrecoverable exceptions) on being subjected to
>> a type-converting test.
> 
> You referring to 'unknown' type returned by typeof operator in Internet
> Explorer, right?

I am referring to any host object.
 
-- 
PointedEars

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

[toc] | [prev] | [next] | [standalone]

#19260

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?

>    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.

[...]

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/

[toc] | [prev] | [next] | [standalone]

#19261

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.

[toc] | [prev] | [next] | [standalone]

#19297

W dniu 2013-04-13 21:31, Thomas 'PointedEars' Lahn pisze:
> Cezary Tomczyk wrote:
[...]
>>>>> 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.

I am disappointed. Instead of simple example from real life you just 
writing "No, you just need to read more carefully".

Regarding "Where “XMLHttpRequest” is not a property of the object 
referred to by “window”, but of another object in the scope chain." - 
again, would be good to provide an example from real life, not just from 
theory. Just for better understanding, not guessing what author of 
response thought about.

>>>     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.

They are theoretical. Give me scenarios that occur in real life, not 
theoretical.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/

[toc] | [prev] | [next] | [standalone]

#19298

Cezary Tomczyk wrote:

> W dniu 2013-04-13 21:31, Thomas 'PointedEars' Lahn pisze:
>> Cezary Tomczyk wrote:
> [...]
>>>>>> 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.
> 
> I am disappointed. Instead of simple example from real life you just
> writing "No, you just need to read more carefully".

Which is exactly what you should do.  You have claimed that „where 
‘XMLHttpRequest’ is not a property of the object referred to by ‘window’”, 
“isHostMethod will return true”.  However, if it is any good, it will return 
a false-value (trivially, “false”).
 
> Regarding "Where “XMLHttpRequest” is not a property of the object
> referred to by “window”, but of another object in the scope chain." -
> again, would be good to provide an example from real life, not just from
> theory. Just for better understanding, not guessing what author of
> response thought about.
> 
>>>>     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.
> 
> They are theoretical. Give me scenarios that occur in real life, not
> theoretical.

An old, weathered bridge was crossing a river from high above.  Someone had 
placed a warning sign before the bridge, saying that if you want to live you 
should not cross it.

One day, a wild animal ran across the bridge, not heeding the warning sign.  
The deck of the bridge crashed instantly, and the animal fell to its death.

A month later, a novice saw the warning sign and asked the master whether 
anyone had actually seen the bridge failing.  The master said they could not 
remember having heard of any incident.  Being confident then that the bridge 
was safe, the novice walked across the bridge carelessly.  Its old, 
weathered deck crashed almost instantly, and the novice fell to their death.

An apprentice heard of that incident, and asked the master what precautions 
should be taken in order to cross such a bridge safely.  The master told 
them.  The apprentice walked across the bridge carefully; still, its deck 
crashed in the middle.  But thanks to their precautions, the apprentice 
survived.

Later that day, as it was in their habit, the master walked down to the 
river and crossed it by the boat they had secured there.  They did not 
remember that they placed the warning sign before the bridge as an 
apprentice years ago, after they almost fell to their death.
 
-- 
PointedEars

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

[toc] | [prev] | [next] | [standalone]

#19258

Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:

> Mikael Andersson wrote:
>
>> jorythompson@gmail.com writes:
>> 
>> [snip]
>>> 
>
> Never do it that way; write templates that you include, as a first step to 
> separate presentation from business logic.  See also: MVC.
>
>>>         while($row = mysql_fetch_array($result)) {
>
> Make it clear that you are evaluating the right-hand side of the assignment:
>
>   while (($row = mysql_fetch_array($result))) {
>

In php its not necessary to do that. But I agree on that it makes things
clearer.

Yours,
QubeX2

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.javascript

csiph-web