Strange behaviour on hook after page render

[Juergen]

Hello

I have discovered a strange issue after running a hook after page render. So this is the hook that I run within the init() method inside a module:

public function init(){
	// add CSS and JS links to the frontend template
    $this->addHookAfter('Page::render', $this, 'addAssets');
}

protected function addAssets(HookEvent $event):void
    {
        $page = $event->object;
        // don't add this to the admin pages
        if ($page->template->name === 'admin') {
            return;
        }
        $version = $this->getModuleInfo()['version'];
        if (!$this->input_removeJS) {

            $js = '<script src="' . $this->wire('config')->urls->$this . 'frontendforms.js?v=' . $version . '"></script>' . PHP_EOL;
            $event->return = str_replace('</body>', $js . PHP_EOL . '</body>', $event->return);
        }
        if (!$this->input_removeCSS) {
            $css = '<link rel="stylesheet" type="text/css" href="' . $this->wire('config')->urls->$this . 'frontendforms.css' . '"/>' . PHP_EOL;
            $event->return = str_replace('</head>', $css . PHP_EOL . '</head>', $event->return);
        }
    }

This hook method adds a javascript script tag and CSS link tag to the page on the frontend. So far so good. It has worked til now until problems. Now I have added this code to a newly created module, but now it does not work in this case. Take a look what Tracy says:

 

You can see the calls of 2 different modules using the same hook after page render code:  The first one is the new module and the second one is from my FrontendForms module. Just to keep in mind: both modules use the same hook and the same hook function to add script and CSS to the frontend.

As you can see, the first module returns "null", but should return a string. The second one (the FrontendForms module) returns a string as expected.

I cannot see any problems via Tracy, so I have no idea, why this happens. The only difference that I can see is on the id key:

'id' => 'Page:100.3:render'

'id' => 'Page:100.0:render'

Does anyone has an idea, what could be the cause, that the first hook returns null instead of a string????

Thanks in advance

[BitPoet]

5 minutes ago, Juergen said:

As you can see, the first module returns "null", but should return a string.

The question is: is $event->return already null when your hook is entered? If yes, the problem happens earlier.

[Juergen]

2 minutes ago, BitPoet said:

The question is: is $event->return already null when your hook is entered? If yes, the problem happens earlier.

I only can confirm that $event->return is null inside the addAssets() method, but I cannot find out, where it probably happens earlier. So the $event variable which will be entered as the parameter inside the brackets has null as return parameter.

Is there way to find out WHERE the problem could be?

 

[bernhard]

You could add something like this to your module that shows null:

if(!$event->return) bd(Debug::backtrace());

The backtrace could have some helpful information what's going on before it is null.

[Juergen]

Thanks! This is an interesting approach, that I have never used before.

This is what I get so far:
 

0 =>array

'file' => 'C:\xampp\webseite1\wire\modules\Process\ProcessPageView.module:184'

'call' => '$page->render()'

1 =>array

'file' => 'C:\xampp\webseite1\wire\modules\Process\ProcessPageView.module:114'

'call' => 'ProcessPageView $process->renderPage(Page $obj, PagesRequest $obj)'

2 =>array

'file' => 'C:\xampp\webseite1\index.php:55'

'call' => 'ProcessPageView $process->execute([ true ])'

1) returns the string as expected -> OK

2) returns the string as expected -> OK

3) returns the string as expected -> OK

 

Unfortunately, every 3 calls return the HTML code as a string as expected, but thank you for this tip - I will keep this in mind for the future ?