JavaScript and Partial Postbacks

There can be some confusion over when to use $(document).ready() vs pageLoad() vs add_init() in JavaScript. It really depends on the situation. The following summary from this old article should help. If you need more details see this MSDN article on AJAX Client Life-Cycle Events.

Using $(document).ready()

• Ideal for one-time initialization.

• Optimization black magic; may run slightly earlier than pageLoad().

• Does not re-attach functionality to elements affected by partial postbacks.

Using pageLoad()

• Unsuitable for one-time initialization if used with UpdatePanels.

• Slightly less optimized in some browsers, but consistent.

• Perfect for re-attaching functionality to elements within UpdatePanels.

Using Sys.Application.add_init( function(){} );

• Useful for one-time initialization if only ASP.NET AJAX is available.

• More work is required to wire the event up.

• Exposes you to the “sys is undefined” error if you aren’t careful.

app.add_load(ApplicationLoad);

app.add_init(ApplicationInit);