jQuery AJAX producing 304 responses when it shouldn't

Question

This really has me scratching my head. Namely because it only happens in IE, not Firefox, and I was under the impression that jQuery was effectively browser neutral. I've been cracking at this thing for the past few hours and have nailed down, at least, what is happening.

This jqGrid:

$("#DocumentListByPartRecordsGrid").jqGrid(           {             datatype: 'local',                         colNames: ['<b>Id</b>', '<b>Document Name</b>', '<b>Document Type</b>', '<b>Effective Date</b>', '<b>Expiration Date</b>', '<b>Delete</b>'],             colModel: [                   { name: 'ASSOCIATION_ID', Index: 'ASSOCIATION_ID', resizable: true, align: 'left', hidden: true, sortable: false },                   { name: 'FILE_NAME', Index: 'FILE_NAME', resizable: true, align: 'left', sortable: false, width:'20%' },                   { name: 'DOCUMENT_TYPE', Index: 'DOCUMENT_TYPE', resizable: true, align: 'left', sortable: false, width:'20%' },                   { name: 'EFFECTIVE_DATE', Index: 'EFFECTIVE_DATE', resizable: true, align: 'left', sortable: false, width:'20%' },                   { name: 'EXPIRATION_DATE', Index: 'EXPIRATION_DATE', resizable: true, align: 'left', sortable: false, width:'20%' },                   { name: 'Delete', Index: 'Delete',resizable: true, align: 'center', sortable: false, width:'20%' },                   ],                         rowNum: 15,             rowList: [15, 50, 100],             imgpath: '/Drm/Content/jqGrid/steel/images',             viewrecords: true,                         height: 162,                        loadui: 'block',             forceFit: true         }); 

Filled by this function:

var mydata = '';     <% if(!string.IsNullOrEmpty(Model.PCAssociatedDocuments)) { %>            var mydata = <%= Model.PCAssociatedDocuments %>; <% } %>  for (var i = 0; i <= mydata.length; i++){         jQuery("#DocumentListByPartRecordsGrid").addRowData(i, mydata[i], "last");         } 

Which is cleanly populated from the model. This is not the issue. The issue arises when using the delete functionality, which is formatted back in the controller like so:

<a class='deleteAttachment' style='cursor: pointer;' href='#' onclick='javascript:PCDocumentDelete(" + s.AssociationId.ToString() + ", " + pcId + ");'>Delete</a> 

and calls this function

function PCDocumentDelete(id, pcid) { if (confirm("Are you sure you want to delete this document?")) {     $.blockUI({         message: "Working...",         css: {             background: '#e7f2f7',             padding: 10         }     });     $.ajax(         {             url: '/DRM/Pc/DeleteAssociation?associationId=' + id + '&pcid=' + pcid,             async: true,             dataType: "json",             success: function(result) {                 if (result.Success == true) {                     //Reload grid                                            $.ajax({ async: false });                     $("#DocumentListByPartRecordsGrid").setGridParam({ url: "/Drm/Pc/DeAssociatePartRecordsWithDocument?pcid=" + pcid, datatype: 'json', myType: 'GET', page: 1 });                     $("#DocumentListByPartRecordsGrid").trigger("reloadGrid");                     $.unblockUI();                     $.showGlobalMessage('Specified document has been successfully disassociated from this part record.');                 }                 else {                     $.unblockUI();                     $.showGlobalMessage('An error occurred deleting the attachment.');                 }             },             error: function(res, stat) {                 alert(res.toString());                 alert(stat.toString());             }         });     return false; } else {     return false; } 

}

(showGlobalMessage is an internal function that creates a particularly formatted blockUI)

The ajax calls a method back in the controller, but the issue arises before we make it that far, so unless someone thinks it important, I'm not going to post that code. What happens is, often for inexplicable reasons, the first burst of ajax that calls PC/DeleteAssociation is coming back with a 304 (not modified) response. I know that happens on a get when nothing has changed that needs to be refreshed. But this isn't a get, it should be treated as a post, and I was under the impression that jquery.ajax was designed to, unless otherwise instructed, not generate 304 responses. I'm obviously missing something here and have been staring at it far too long to catch it myself. Anyone see what I missed? Thank you.

Answer 1

I cannot see, you specifying the ajax request as a POST. So basically add:

$.ajax({ type: 'POST' }); 

and if that still fails (due to some browser AJAX weirdness), you could try setting cache: false:

$.ajax({ type: 'POST', cache: false }); 

Btw, all cache: false does, is adding some random stuff to the request URL.

EDIT1:

Regarding the

... and I was under the impression that jquery.ajax was designed to, unless otherwise instructed, not generate 304 responses

jQuery istn't generating any responses here. And the 304-header is just an HTTP header. HTTP AJAX requests are ordinary HTTP requests and may return any valid header. If the server responds with 304, the XHR object will simply serve up the locally cached response from the server. It's completely transparent for the user, though.

EDIT2:

Removed the advice about preventing caching. Seems like Voodoo to me.

EDIT3:

Added that bit in again because it apparently was necessary. Looking around the web, IE seems to be illegally caching AJAX POSTs to some extent.

Answer 2

1. Always use POST for calls to methods that modify state, not GET. This should be enough in this instance to prevent IE caching the request.
2. IE aggressively caches ajax requests (see http://www.dashbay.com/2011/05/internet-explorer-caches-ajax/ and https://blog.httpwatch.com/2009/08/07/ajax-caching-two-important-facts/). To prevent this, you can:
   1. Add a cache busting parameter ($.ajaxSetup({ cache: false }); does this automatically.
   2. Always use POST requests (probably not appropriate in most cases).
   3. Turn on cache headers for AJAX requests server side. The first link demonstrates how to do this using in groovy. Similar methods should apply to any framework.