How to inject pure javascript into head in Magento 1.9 extension? - magento

Question

I'm developing a Magento extension that deals with analytics. One of the things it needs to do is pass events (such as checkout_cart_add_product_complete and catalog_controller_product_view) from the backend PHP observer class to the frontend javascript.
I have the events working in myextension's config.xml:
<events>
...
<catalog_controller_product_view>
<observers>
<myextension>
<type>model</type>
<class>myextension/observer</class>
<method>productViewContent</method>
</myextension>
</observers>
</catalog_controller_product_view>
<checkout_cart_add_product_complete>
<observers>
<myextension>
<type>model</type>
<class>myextension/observer</class>
<method>productAddToCart</method>
</myextension>
</observers>
</checkout_cart_add_product_complete>
...
</events>
I have the Observer.php model implemented to write to the log currently:
public function productViewContent($observer) {
$product = $observer->getProduct();
Mage::log('('.$product->getId() .') '. $product->getName().' has been viewed.', null, 'product.log');
}
public function productAddToCart($observer) {
$product = $observer->getProduct();
Mage::log('('.$product->getId() .') '. $product->getName().' has been added to cart.', null, 'product.log');
}
and I'm seeing the correct product details in the product.log.
Now where I am stuck is in this class:
class Mynamespace_Myextension_Block_Html_Head extends Mage_Page_Block_Html_Head {
// some session code here
$this->addJs('myextension/file.js');
}
I've successfully detected that myextension/file.js is loading, but I need to be able to pass dynamic event info to the JS file. I was hoping to be able to do something like:
class Mynamespace_Myextension_Block_Html_Head extends Mage_Page_Block_Html_Head {
// some session code here
$this->addRawHTML('<script>var myevent='addtocart';var myproduct=$product_id</script>');
$this->addJs('myextension/file.js');
}
...so that myevent and myproduct are available to the code that runs in file.js. Obviously there is no such method addRawHTML.
Hopefully that makes sense. I tried
echo "<script>alert('add_to_cart');</script>";
in the my extension's Head.php block and I get the alert as expected, but it of course is printed before the first line of the html which is not the correct way to do it.
Also, I am currently using the session to write details about the event from the Observer so that the _prepareLayout method in Mynamespace_Myextension_Block_Html_Head can read them and forward them on to the JS in the layout. Is there a better way?
In a nutshell, I'm not able to modify layout.xml/theme.xml because this is an extension, and I'm not able to use addJs alone because I need the JS file to be dynamically generated or detect JS variables written dynamically into the page.
Is it considered bad practice to call add JS with a PHP file?
$this->addJs('myextension/file.php?myevent=add_to_cart&product_id='.$product_id);
and render the JS file dynamically using PHP? That might work but it seems like a hack.
Thanks for your advice.
UPDATE: I have managed to get something working, but in a "non-magento-way". I followed something like this answer, basically generating Javascript on the fly from the observer directly:
public function generateLayout($observer)
{
// I do this if there's an event in a custom session variable
$layout = $observer->getEvent()->getLayout();
$headBlock = $layout->getBlock('head');
$block = $layout->getBlock('head');
$block->setText("
<script>
var myevent = '$event';
var myproduct = '$product';
</script>
");
$headBlock->append($block);
}
I would still like to approach it properly using Magento best practice.

Answer 1

As you might know, Magento uses a javascript variable var spConfig (in view pages) for storing product data to be used in javascript for changing prices and other thigs.
Can't you use such a js variables that store product/cart info and use them in js file that you are including (that is file.js)