If you like to fix any details for your customer on the checkout page and do not like to be updated by the customer then here is how you can fix that:
You can not use disabled attribute as most of the fields are required and Disabled <input> elements in a form will not be submitted! so readonly attribute is the preferred method here.
readonly can only be applied on text and textarea in HTML so to fix the value of dropdown like country or state please refer to our other tutorial.
If you like to fix all the fields on the checkout form. Let’s suppose customer placing the additional order which may confuse you if he has filled different details then you can fix/disable all the fields using the foreach loop under the same hook as shown here.