Sometimes, people ask me how to handle session management within an application that makes AJAX requests. A question like this can mean many different things; but often times, after a little discussion, I discover that this question is based on a fundamental misunderstanding of what an AJAX request actually is. Because we are so used to the request-response life cycle, there is something almost magical about an AJAX request that runs in parallel to the page processing; heck, I use them all the time and I still get a jolt of delight at seeing them work. In reality, however, there is nothing magical about them; in fact, they work exactly like every other HTTP request.
Because HTTP is an inherently stateless protocol, we generally rely on cookies to maintain the state of a user's session across multiple HTTP requests. However, since there is still a bit of mystery surrounding AJAX requests, people are sometimes not sure as to whether or not cookies play nicely with AJAX. But, once you accept the fact that an AJAX request is an HTTP request, it becomes a no-brainer that cookies get sent back and forth in the AJAX request-response headers.
To demonstrate this functionality, I have put together a little ColdFusion demo that executes an AJAX request and outputs the cookies that the AJAX request posted to the server. And, to show that cookies can be both send and set, I am also generating a new cookie with each AJAX request.
I have tested this demo in the following browsers:
- IE 6,7,8
Here is the server-side page that is responding to the incoming AJAX request:
Get.cfm (AJAX End Point)
<!--- Create a response that outputs all of the cookies currently passed in from the AJAX request. In ColdFusion, the cookie collection is populated by the request headers. ---> <cfsavecontent variable="responseText"> <cfoutput> <h3> Cookies ( as of #timeFormat( now(), "hh:mm:ss" )# ) </h3> <ul> <!--- Loop over the cookie collection. ---> <cfloop item="key" collection="#cookie#"> <!--- Only output cookies relevant to this test. ---> <cfif reFindNoCase( "^rand", key )> <li> #key# : #cookie[ key ]# </li> </cfif> </cfloop> </ul> </cfoutput> </cfsavecontent> <!--- Now that we've created the cookie output, let's create a random cookie to set in the current AJAX request. This will get sent back to the client as Set-Cookie header. ---> <cfcookie name="rand#randRange( 111, 999 )#" value="Woot!" /> <!--- Return the HTML response to the client. ---> <cfcontent type="text/html" variable="#toBinary( toBase64( responseText ) )#" />
As you can see, this ColdFusion code is simply echoing back (in HTML format) the cookie collection that the AJAX request has posted. And, to demonstrate that cookies can also be set from within an AJAX request, I am generating a new cookie with the CFCookie tag.
Here is the test HTML page that is making the AJAX request:
As you can see, all we're doing here is making a AJAX request and appending the HTML response to the page. In this way, we can see how the collection of cookies gets mutated over time.
NOTE: I am making a synchronous request, rather than an asynchronous request, such that I don't have to worry about a ReadyState change handler.
After clicking the "Test AJAX Request" link a few times, here is the page output that I get:
As you can see, the collection of cookies is being augmented with every single AJAX request. This clearly demonstrates that AJAX requests both send the existing cookie collection and correctly respond to Set-Cookie headers within the AJAX response.
I believe that there are ways to make cookies explicitly unavailable for AJAX requests; I think IE has a proprietary "HTTPOnly" attribute or something - I know very little about that. But, other than that and a few IFrame bugs, I hope this demonstration makes people feel a little more comfortable using session management in the context of AJAX requests. Just remember - AJAX requests are HTTP requests.
Want to use code from this post? Check out the license.