Seems to me that AJAX before document-ready could get complicated once you want to actually do something with the response. Normally one would do something like this: $(document).ready(function(){ $.getJSON(my_url, function(data) { $(' ').text(data.some_text).appendTo('#some_container); }); }); But if we call getJSON before document-ready, the node $('#some_container') may not yet exist! Now we need some way to wait…
The way browsers implement both JavaScript and document rendering via a single-threaded execution queue, that isn't an issue. Once the page begins rendering, callbacks won't have a chance to execute until after the document is rendered and ready. That's the same mechanism that makes the setTimeout(fn, 0) trick work, for example.
It feels a bit like driving fast with no seat belt on, but it's safe.
If you do want to be extra cautious, MBlume's suggestion to wrap the success handler in $(document).ready() works fine too. That's effectively the same as not wrapping it.