Magento 2 : Add custom script just after head tag
I am not sure if this is the correct way or not, but I have got a lead.
By default magento 2 usees the root.phtml file to setup head content accordingly, which is located in vendor/magento/module-theme/view/base/templates/root.phtml (if it has not been overridden).
Here, the $requireJs variable is loaded first in the head block. The $requireJs variable is defined in the render method inside Page class -which is located in vendor/magento/framework/view/Result/Page.php.
In this file, $requireJs contains the require.js block. And the require.js block is defined in vendor/Magento/module-theme/view/frontend/layout/default.xml :
<block name="require.js" class="Magento\Framework\View\Element\Template" template="Magento_Theme::page/js/require_js.phtml" />Solution
1) Copy require_js.phtml from vendor/magento/module-theme/view/frontend/templates/page/js to your theme app/design/frontend/{VENDOR}/{THEME_NAME}/Magento_Theme/templates/page/js/
2) Now you can add your script like this:
<script> console.log("I'm loaded!"); var require = { "baseUrl": "<?php /* @escapeNotVerified */ echo $block->getViewFileUrl('/') ?>" };</script>UPDATE (Using Module)
Overriding the require.js block is not an elegant solution. if anyone has a good solution please answer. For now edit your layout xml:
<referenceBlock name="require.js"> <action method="setTemplate"> <argument name="template" xsi:type="string">Custom_Module::success/head.phtml</argument> </action></referenceBlock> and inside success/head.phtml add your code:
<script> console.log("I'm loaded!"); var require = { "baseUrl": "<?php /* @escapeNotVerified */ echo $block->getViewFileUrl('/') ?>" };</script>
I found a simple way of doing it that seems very reasonable, because it uses existing features in the adminhtml theme without any need to override/intercept anything.
Background
Like @sanchit-gupta mentioned, the root.phtml template is used as the basis to render both the frontend and adminhtml areas, and so is the associated class \Magento\Framework\View\Result\Page, which always looks for a block named head.additional before rendering.
This block exists in the frontend layouts by default, but unfortunately it doesn't exist in the adminhtml layout.
Solution
With that in mind, the current best way (as of 2.3.x) to add inline <scripts> to the adminhtml's <head> section is to add any head.additional block: it will be automatically rendered by the framework. It either has to be a ListText block so that it renders all it's children automatically, or a Template with a specified template file. I actually chose too nest my actual block inside the ListText block just to keep the same mechanism available as in the frontend area (i.e. for compatibility with other plugins that might be doing the same).
Example
In your custom module or theme, add a layout update that inserts the following block into the body of the page layout (which is just to do it the same way as it's done in Magento 2 core for the frontend area):
<body> <block class="Magento\Framework\View\Element\Text\ListText" name="head.additional"> <block name="your_block" class="Magento\Framework\View\Element\Template" template="Your_Module::your/template.phtml" /> </block></body>Done! Your template will render inside <head></head> – without any awkward overrides or "hacks".
What's more, if other modules also reference head.additional in the adminhtml area, they will be compatible with your code.