Is it necessary to have the script tag as the first tag in the body of the HTML?

I have a script file that needs to be included by third party implementors on their web pages.

It is crucial for this script to be the first tag within the body element, like so:

<body>
<script type="text/javascript" src="/my_script.js"></script>
...

How can I achieve this without relying on any third party libraries?

The purpose of this script is to prevent clickjacking and ensure it runs before the page is rendered. If the script tag is not placed correctly, I want to display an error message alerting the developer to insert it as the first tag in the body.

EDIT: This script's main function is to protect against clickjacking by hiding the entire document if the embedding site is not whitelisted. It is recommended to place it close to the beginning of the body to avoid interference from other scripts and ensure nothing clickable appears before its execution. While not absolutely mandatory, placing it near the top improves effectiveness. This strategy is inspired by suggestions from Owasp's Clickjacking Defense Cheat Sheet, aiming for simplicity and ease of implementation.

javascript

Answer №1

Primary element located within body

If you want to place this code in /my_script.js:

if (document.body.firstElementChild == document.currentScript) {
    // This is the first element
} else {
    // Not the first element
}

I'm uncertain about the reason why you would need to perform this action, but here are the steps to do so.

Relocate script to initial position

To move the script:

document.body.insertBefore(document.currentScript, document.body.firstChild);
document.currentScript.parentElement.removeChild(document.currentScript);

Determine if script is the first one

if (( document.scripts || document.getElementById('script') )[0] == document.currentScript)

Answer №2

It seems unusual that you would have a specific requirement to be the very first tag after the body element, but let's put that aside for now and focus on addressing your technical inquiry. By utilizing the query document.body.childNodes, you can access the nodes that have been loaded up to this point. This data can help you determine whether or not your element is positioned at the beginning of the sequence.

Answer №3

$(document).on("pagecreate",function(){ //execute loading tasks }

this event will be activated prior to the page being displayed.

sources :

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