@laoneo can you please have a Look?

The display of fields (their ... ->value property) is always created twice
aka the layout will be loaded twice

• once for automatic display via a configurable event (this can be disabled) and
• once for manual display (onContentPrepare event) (there is no option to disable this)

See the PR linked below for explanation and for discussion,
about option to disable manual creation , it was decided to be a B/C break or something

[com_fields] Fix fields display HTML prepared 4 or 5 times per article, make it be prepared only twice
#17895

@ggppdk thanks for Comment, so Issue can be closed as expected Behaviour?

@tassosm set a break point in your tmpl. Where do the two different calls do come from?

You can create a js file include it through jhtml::script();. There problem solved

To explain a little better my suggestion above: joomla doesn’t have any way to force uniqness on inclusion of inline scripts. The only way to assure you will only load once an asset is through jhtml script for a static js file. There are way too many pitfalls in the architecture here that needs to be patched and is far easier to just say use always js files for your scripts than try to fix wrong architecture decisions (which maybe dated to mampo era).
Anyways my 2c

@laoneo
i checked layout is loaded once, did something change ? some magic method for manual display or other change ?

Ok what i wrote above applies,
the layout is loaded twice as expected ...

once for automatic display via a configurable event (this can be disabled) and
once for manual display (onContentPrepare event) (there is no option to disable this)

just the output is captured, lol, i forgot of it
so you can not print a back-trace in it, instead you should log it to a file or ... use a debugger

Manual display (in case they are needed)

#5  PlgSystemFields->onContentPrepare() called at [libraries\joomla\event\event.php:70]
#6  JEvent->update() called at [libraries\joomla\event\dispatcher.php:160]
#7  JEventDispatcher->trigger() called at [components\com_content\views\article\view.html.php:193]

Automatic display (according to configuration, e.g. in my case set to onContentBeforeDisplay)

#6  PlgSystemFields->onContentBeforeDisplay() called at [libraries\joomla\event\event.php:70]
#7  JEvent->update() called at [libraries\joomla\event\dispatcher.php:160]
#8  JEventDispatcher->trigger() called at [components\com_content\views\article\view.html.php:199]

Back-trace in log file

#0  include() called at [administrator\components\com_fields\libraries\fieldsplugin.php:131]
#1  FieldsPlugin->onCustomFieldsPrepareField() called at [libraries\joomla\event\event.php:70]
#2  JEvent->update() called at [libraries\joomla\event\dispatcher.php:160]
#3  JEventDispatcher->trigger() called at [administrator\components\com_fields\helpers\fields.php:201]
#4  FieldsHelper::getFields() called at [plugins\system\fields\fields.php:479]
#5  PlgSystemFields->onContentPrepare() called at [libraries\joomla\event\event.php:70]
#6  JEvent->update() called at [libraries\joomla\event\dispatcher.php:160]
#7  JEventDispatcher->trigger() called at [components\com_content\views\article\view.html.php:193]
#8  ContentViewArticle->display() called at [libraries\src\MVC\Controller\BaseController.php:672]
#9  Joomla\CMS\MVC\Controller\BaseController->display() called at [components\com_content\controller.php:113]
#10 ContentController->display() called at [libraries\src\MVC\Controller\BaseController.php:710]
#11 Joomla\CMS\MVC\Controller\BaseController->execute() called at [components\com_content\content.php:43]
#12 require_once(components\com_content\content.php) called at [libraries\src\Component\ComponentHelper.php:382]
#13 Joomla\CMS\Component\ComponentHelper::executeComponent() called at [libraries\src\Component\ComponentHelper.php:357]
#14 Joomla\CMS\Component\ComponentHelper::renderComponent() called at [libraries\src\Application\SiteApplication.php:194]
#15 Joomla\CMS\Application\SiteApplication->dispatch() called at [libraries\src\Application\SiteApplication.php:233]
#16 Joomla\CMS\Application\SiteApplication->doExecute() called at [libraries\src\Application\CMSApplication.php:195]
#17 Joomla\CMS\Application\CMSApplication->execute() called at [index.php:49]


#0  include() called at [administrator\components\com_fields\libraries\fieldsplugin.php:131]
#1  FieldsPlugin->onCustomFieldsPrepareField() called at [libraries\joomla\event\event.php:70]
#2  JEvent->update() called at [libraries\joomla\event\dispatcher.php:160]
#3  JEventDispatcher->trigger() called at [administrator\components\com_fields\helpers\fields.php:201]
#4  FieldsHelper::getFields() called at [plugins\system\fields\fields.php:388]
#5  PlgSystemFields->display() called at [plugins\system\fields\fields.php:325]
#6  PlgSystemFields->onContentBeforeDisplay() called at [libraries\joomla\event\event.php:70]
#7  JEvent->update() called at [libraries\joomla\event\dispatcher.php:160]
#8  JEventDispatcher->trigger() called at [components\com_content\views\article\view.html.php:199]
#9  ContentViewArticle->display() called at [libraries\src\MVC\Controller\BaseController.php:672]
#10 Joomla\CMS\MVC\Controller\BaseController->display() called at [components\com_content\controller.php:113]
#11 ContentController->display() called at [libraries\src\MVC\Controller\BaseController.php:710]
#12 Joomla\CMS\MVC\Controller\BaseController->execute() called at [components\com_content\content.php:43]
#13 require_once(components\com_content\content.php) called at [libraries\src\Component\ComponentHelper.php:382]
#14 Joomla\CMS\Component\ComponentHelper::executeComponent() called at [libraries\src\Component\ComponentHelper.php:357]
#15 Joomla\CMS\Component\ComponentHelper::renderComponent() called at [libraries\src\Application\SiteApplication.php:194]
#16 Joomla\CMS\Application\SiteApplication->dispatch() called at [libraries\src\Application\SiteApplication.php:233]
#17 Joomla\CMS\Application\SiteApplication->doExecute() called at [libraries\src\Application\CMSApplication.php:195]
#18 Joomla\CMS\Application\CMSApplication->execute() called at [index.php:49]

@laoneo the 2nd call is coming from the Automatic Display option as @ggppdk described very well.

@dgrammatiko loading a script file seems to be the only solution here, indeed. However, in my case, seems like an overkill to use a script file for just two lines of code.

You will be then CSP compliant. Another benefit, even for two lines.

@tassosm , also a static variable should work

static $layout_scripts_added = null;

if ($layout_scripts_added === null)
{
	$layout_scripts_added = true;
	JFactory::getDocument()->addScriptDeclaration('
		alert("Hello world!");
	');
}

You will be then CSP compliant. Another benefit, even for two lines.

You can do CSP compliance with inline scripts (without exclusion rules), that's where nonce's come into play (do we have that capability in our CSP code yet, haven't really looked deep at it).

And a reminder here
layouts (whatever their type is ...) are reused

even if you eliminate the double loading of the layout file for this particular field instance

there are still legitimate reasons to load it multiple times
e.g. you have 3 fields of type 'myfieldtype', and you display all 3 fields
then layout file should be loaded at least 3 times

or even you may set a modified value or configuration to the field and call API to recreate it is display
e.g. display a value in format A and then also in format B

[EDIT]
probably you wanted to add the script once per field instance, in that case my comment above is not applicable

Set to "closed" on behalf of @jwaisner by The JTracker Application at issues.joomla.org/joomla-cms/21004

Closing as expected behavior.