If you're using the Magento 2 Mega Menu extension, there may be certain cases in which you see an error in the console that looks something like this:
The error will usually result in a lack of functionality in the menu section of the store, such as an inability to drop down the menu and view the subcategories.
The cause of the error is usually a conflict with a 3rd party module and happens because the Mega Menu and the 3rd party extension a mixin to the menu.js file. The solution here would be to edit the code of the 3rd party module's mixin.js file as follows:
Note: This modification should be applied via the standard Magento customization process, whereby the edited file is extended so as to avoid it being overwritten when the 3rd party module is updated.
After making and saving the change, redeploy the static content and flush all your available caches. The functionality should then be restored.