Question: I'm working on a codebase with multiple blocks of code setting some behavior on document.ready() (jQuery). Is there a way to enforce that one specific block is called before any of the others? 

Background:
I need to detect JS errors in an automated testing environment, so I need the code that starts logging JS errors to execute before any other JS code executes.

Answer: 
`document.ready()` callbacks are called in the order they were registered. If you register your testing callback first, it will be called first.

Also if your testing code does not actually need to manipulate the DOM, then you may be able to run it as the code is parsed and not wait until the DOM is ready which would run before the other `document.ready()` callbacks get called. Or, perhaps you could run part of your testing code immediately and defer only the part that uses the DOM until `document.ready()`.

Another idea is (for testing purposes only) you could run with a slightly modified version of jQuery that added a flag to `document.ready()` that when passed and set to `true` indicated to call that function first or you could add a new method `document.readyFirst()` that would call your function first. This would involve minor changes to the `document.ready()` processing code in jQuery.
As @jfriend00 mention that `ready callbacks are called in the order they were registered.`

So even if this code block called on the beginning, you can set another callback in it so it'll be executed on endmost.

```js
jQuery(document).ready(function(){
    jQuery(document).ready(function(){
        // This block will be executed after all ready calls.
    });
});

```