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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: trying to disable a text input field when a particular select list option is selected in a select field but this code has no effect
Date: Mon, 30 Nov 2015 22:43:03 +0100
Organization: PointedEars Software (PES)
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Stefan Weiss wrote:

> On 2015-11-30 05:23, fugee279@gmail.com wrote:
>> <script>
>> $(document).ready(function () {
>>   $('#select_field').change(function(e)

If you must use jQuery, use

  $("#select_field").on("change", function(e) {
    // …
  });

instead.  That code is more efficient (it avoids another wrapper), cleaner 
(event registrations are easy to spot as they look the same), and easier to 
maintain (you can append new event types to the string value).

Also, be as consistent as possible in your string delimiters.  Not only 
makes that code easier to read, but also easier to maintain.

>>    {
>>     if (e.target.value=='select_value') {e.second_field.disabled = true;}
>>   })
>> })
>> </script>
> 
> Next time, please include the error message you see in the console.
> 
> The parameter `e` is the Event object for the change event. This object
> doesn't have a "second_field" property.

Since it is _not_ a reference to an object implementing only the Event 
interface of W3C UI Events, but to a *jQuery* event object, it could have 
that property.

<http://www.w3.org/TR/2015/WD-uievents-20150428/#event-types>
<http://api.jquery.com/category/events/event-object/>

Usually one would send the information in the jQuery event’s extraParameters 
when .trigger()ed, though:

<http://api.jquery.com/trigger/>

> Not knowing what your document looks like, I can only guess at a
> solution... possibly
> 
>     $("#second_field").prop("disabled", true);

Or, much more efficient:

  document.getElementById("second_field").disabled = true;

See also:

<https://gist.github.com/chitsaou/3066411>
<http://youmightnotneedjquery.com/>

-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | SVN: <http://PointedEars.de/wsvn/>
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