How to make all the textarea disabled used as ckeditor

How to make all the textarea disabled used as ckeditor

I have a set of textareas which are used as editors. I want to make those
textareas readonly in some condition. I am able to do it for individual
textareas.
$("#txtHtmlHead").ckeditorGet().setReadOnly();
but when looping through each textareas is not working
$('textarea').each(function() {
$(this).ckeditorGet().setReadOnly();
});
I am getting the below exception
CKEditor is not initialized yet, use ckeditor() with a callback.
Can anybody help?