TypeError when loading the javascript

[Schlumpf9]

When I run your script in head I get the following error:
TypeError: document.body is null

To fix this you have to put the js code below the body tag. Is there any other fix to have the js in the head section? This appears in firefox and chrome.

[ghost]

This kind of issue often happen when you're trying to interact with the DOM when it is not properly loaded (i.e. too soon).

You can add an event listener in order to wait until the DOM is fully loaded before interact with it.

You can use $.ready(function(){/* your code here */}) with jquery or document.addEventListener('DOMContentLoaded', function(){/* your code here */}) in native javascript.

Thus, your javascript code will wait the end of the page load to add your notification system.

[dominique-mueller]

The easiest way is to load the library with a "defer" attribute attached. For example:

<script src="notification.min.js" defer></script>

For details, see https://www.w3schools.com/tags/att_script_defer.asp