Insert JavaScript block on product pages via Observer

Question

I'm trying to add console.log() to specific page types such as product_view or onepage_success. However, I am encountering difficulties doing so. I'm trying to use an event observer to check which page type I am running:

config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
...
    <global>
        <models>
            <my_module>
                <class>My_Module_Model</class>
            </my_module>
        </models>
    </global>
    <frontend>
        <events> 
            <controller_action_postdispatch_catalog_product_view>
                <observers>
                    <my_module_addjs>
                        <type>singleton</type>
                        <class>my_module/observer</class>
                        <method>addJavascriptBlock</method>
                    </my_module_addjs>
                </observers>
            </controller_action_postdispatch_catalog_product_view>
        </events>   
    </frontend>
</config>

Observer.php

<?php
class My_Module_Model_Observer {
    public function addJavascriptBlock($observer) {
        $controller = $observer->getAction();
        $controller_name = Mage::app()->getFrontController()->getRequest()->getControllerName();
        $controller_action = Mage::app()->getFrontController()->getRequest()->getActionName();
        if ($controller_name === 'product' && $controller_action === 'view') {
            $this->appendJS($controller);
        } 
    }

    private function appendJS($controller) {
        $layout = $controller->getLayout();
        $block = $layout->createBlock('core/text');
        $block->setText(
        '<script type="text/javascript">
            function hello() {
                console.log("Foo");
            }
            hello();
        </script>'
        );        
        $layout->getBlock('head')->append($block);  
    }
}

For which I get Fatal error: Call to a member function getLayout() on a non-object in $layout = $controller->getLayout();

If I use the controller_action_layout_generate_blocks_after event, it works. Any ideas why this happens? Is controller_action_postdispatch_* being fired before the layout gets initialised?

Answer 1

Any particular reason you are not using layout update file (e.g. local.xml) to add your javascript? Seems easier that way.

Anyways, controller_action_postdispatch_*** fires after HTML has been generated, so it's not possible to change layout at that point anymore.

You should use controller_action_layout_render_before_*** event. To get layout object in your observer, simply call Mage::app()->getLayout();