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Wednesday, June 17, 2009

AJAX Callback to ASP.NET Using jQuery

jQuery is just a JavaScript library so it will work seamlessly with ASP.NET both from page code as well as through backend driven code using the Page.ClientScript object or ScriptManager. You can use jQuery on its own as a client side and AJAX library that communicates with ASP.NET or you can use jQuery in combination with ASP.NET AJAX. The two actually complement each other quite well as jQuery provides functionality that the ASP.NET AJAX library does not and vice versa. For the most part the interaction between the two libraries is trouble free except for a few very rare edge cases.

One of the most obvious client-side features of any JavaScript client library is the ability to make AJAX calls to the server. jQuery includes a host of AJAX functions that make it easy to retrieve content from a URL in a variety of ways. Here’s a list of some of the functions available:


This the low-level AJAX function with many, many options that lets you create just about any kind of AJAX request. If you need full control over requests or you want to create a generic component that calls back to the server (like the WCF/ASMX client proxy I’ll discuss later) you’ll want to use this function. For now check out the documentation ( on the multitude of options available.


The .load() function is the only AJAX function that works off a jQuery selector. It calls a URL on the server and loads the result as content into selected element(s). It’s a very quick and easy way to load HTML fragments and inject them into the client HTML document. You can provide an optional callback to be notified with the server result text when the callback completes, which is useful if you want to visually adjust the retrieved content-like applying an effect to visually cue the user to an update.


These functions are simple helpers that provide basic get and post operations to the server. You specify a URL and a callback, which is called with the HTTP response from the server. $.post() also allows you to pass either a formatted POST buffer string or an object the properties of which are turned into POST encoded key value pairs.


Similar to $.post(), but expects the result to be JSON which is automatically deserialized into a JavaScript value and passed to the callback as a parameter. While this function is handy for simple JSON results there are two things to watch out for: Dates are not parsed since there’s no date literal in JavaScript, so whatever the server returns will be used (typically a string). $.getJSON() also doesn’t support JSON POST data-only POST encoded variables. There’s no built-in JSON serialization. $.getJson() function is useful for simple JSON results returned from arbitrary services, but not usable for calling WCF or ASMX ASP.NET services since they expect JSON POST input. I’ll write more on this later in the article.

.getJSON() also supports cross-domain JSONP callbacks. If you specify a query string parameter of callback=? you can force the result to be routed to the callback you specify in the parameter list.


This function loads script code from the server and executes it once downloaded if you haven’t specified a callback. If specified, jQuery fires the optional handler instead and passes the JavaScript, plus the current AJAX request. This can be useful for JSONP cross-domain callbacks where you have no control over the parameters used.

Global AJAX Events

There are also a number of global AJAX events that you can take advantage of, all of which take callbacks as parameters: ajaxCallback(), ajaxError(), ajaxSend(), ajaxStart(), ajaxStop(), and ajaxSuccess(). These are useful for setting up global handlers that can centrally manage AJAX requests. You’re not likely to need these much unless you build components that need to know status of requests.

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