$(document).ready() vs pageLoad() vs Application.Init

jQuery’s $(document).ready()

    * Ideal for onetime initialization.
    * Optimization black magic; may run slightly earlier than pageLoad().
    * Does not re-attach functionality to elements affected by partial postbacks.

ASP.NET AJAX’s pageLoad()

    * Unsuitable for onetime initialization if used with UpdatePanels.
    * Slightly less optimized in some browsers, but consistent.
    * Perfect for re-attaching functionality to elements within UpdatePanels.

ASP.NET AJAX’s Application.Init

    * Useful for onetime initialization if only ASP.NET AJAX is available.
    * More work required to wire the event up.
    * Exposes you to the “sys is undefined” error if you aren’t careful. For this error, see this post
       http://www.aspmemo.net/2011/12/how-to-solve-sys-is-undefined-error.html


Original Post : http://encosia.com/document-ready-and-pageload-are-not-the-same/