最近在项目中遇到一个非常棘手的问题，就是在为页面设置了document.domain时，ajaxfileupload出现跨域错误，究其原因是页面的domain被设置为网站根域（如qingniao.it）时，而ajaxfileupload post到的目标页面的域并非根域，而是一个二级的类似test.qingniao.it的域名，因此会引发无权限的错误。
花了2天的时间终于解决这个问题。
修改后的ajaxfileupload关键代码如下：
jQuery.extend({ createUploadIframe: function(id, uri) { //create frame var frameId = 'jUploadFrame' + id; var iframeHtml = '<iframe id="' + frameId + '" name="' + frameId + '" style="position:absolute; top:-9999px; left:-9999px"'; if (window.ActiveXObject) { if (typeof uri == 'boolean') { iframeHtml += ' src="' + 'javascript:false' + '"'; } else if (typeof uri == 'string') { iframeHtml += ' src="' + uri + '"'; } } iframeHtml += '></iframe>'; jQuery(iframeHtml).appendTo(document.body); return jQuery('#' + frameId).get(0); }, createUploadForm: function(id, fileElementId, data, crossDomain) { //create form var formId = 'jUploadForm' + id; var fileId = 'jUploadFile' + id; var form = jQuery('<form action="" method="POST" name="' + formId + '" id="' + formId + '" enctype="multipart/form-data"></form>'); if (data) { if(Object.prototype.toString.call( data ) === '[object Array]'){ for (var i in data) { jQuery('<input type="hidden" name="' + data[i].name + '" value="' + data[i].value + '" />').appendTo(form); } } else { for (var i in data) { jQuery('<input type="hidden" name="' + i + '" value="' + data[i] + '" />').appendTo(form); } } } if(crossDomain) { try{document.domain=window.location.hostname.split('.').reverse().slice(0,2).reverse().join('.');}catch(e){} jQuery('<input type="hidden" name="callback" />').val("<script type='text/javascript'>try{document.domain=window.location.hostname.split('.').reverse().slice(0,2).reverse().join('.');}catch(e){}</script>").appendTo(form); } var oldElement = jQuery('#' + fileElementId); var newElement = jQuery(oldElement).clone(); jQuery(oldElement).attr('id', fileId); jQuery(oldElement).before(newElement); jQuery(oldElement).appendTo(form); //set attributes jQuery(form).css('position', 'absolute'); jQuery(form).css('top', '-1200px'); jQuery(form).css('left', '-1200px'); jQuery(form).appendTo('body'); return form; }, ajaxFileUpload: function(s) { //handle error var handleError = function(s, xhr, status, e) { // If a local callback was specified, fire it if (s.error) s.error(xhr, status, e); // Fire the global callback if (s.global) jQuery.event.trigger("ajaxError", [xhr, s, e]); }; // TODO introduce global settings, allowing the client to modify them for all requests, not only timeout s = jQuery.extend({}, jQuery.ajaxSettings, s); var id = new Date().getTime(); var form = jQuery.createUploadForm(id, s.fileElementId, (typeof(s.data) == 'undefined' ? false: s.data), s.crossDomain); var io = jQuery.createUploadIframe(id, s.secureuri); var frameId = 'jUploadFrame' + id; var formId = 'jUploadForm' + id; // Watch for a new set of requests if (s.global && !jQuery.active++) { jQuery.event.trigger("ajaxStart"); } var requestDone = false; // Create the request object var xml = {}; if (s.global) jQuery.event.trigger("ajaxSend", [xml, s]); // Wait for a response to come back var uploadCallback = function(isTimeout) { var io = document.getElementById(frameId); var execontent = function(){ try { if (io.contentWindow) { xml.responseText = io.contentWindow.document.body ? io.contentWindow.document.body.innerHTML: null; xml.responseXML = io.contentWindow.document.XMLDocument ? io.contentWindow.document.XMLDocument: io.contentWindow.document; } else if (io.contentDocument) { xml.responseText = io.contentDocument.document.body ? io.contentDocument.document.body.innerHTML: null; xml.responseXML = io.contentDocument.document.XMLDocument ? io.contentDocument.document.XMLDocument: io.contentDocument.document; } } catch(e) { handleError(s, xml, null, e); } if (xml || isTimeout == "timeout") { requestDone = true; var status; try { status = isTimeout != "timeout" ? "success": "error"; // Make sure that the request was successful or notmodified if (status != "error") { // process the data (runs the xml through httpData regardless of callback) var data = jQuery.uploadHttpData(xml, s.dataType); // If a local callback was specified, fire it and pass it the data if (s.success) s.success(data, status); // Fire the global callback if (s.global) jQuery.event.trigger("ajaxSuccess", [xml, s]); } else handleError(s, xml, status); } catch(e) { status = "error"; handleError(s, xml, status, e); } // The request was completed if (s.global) jQuery.event.trigger("ajaxComplete", [xml, s]); // Handle the global AJAX counter if (s.global && !--jQuery.active) jQuery.event.trigger("ajaxStop"); // Process result if (s.complete) s.complete(xml, status); jQuery(io).unbind(); setTimeout(function() { try { jQuery(io).remove(); jQuery(form).remove(); } catch(e) { handleError(s, xml, null, e); } }, 100); xml = null; } }; if(s.crossDomain) { var timer = window.setTimeout(function(){ try{ execontent(); }catch(e){} },1000); } else { execontent(); } }; // Timeout checker if (s.timeout > 0) { setTimeout(function() { // Check to see if the request is still happening if (!requestDone) uploadCallback("timeout"); }, s.timeout); } try { var form = jQuery('#' + formId); jQuery(form).attr('action', s.url); jQuery(form).attr('method', 'POST'); jQuery(form).attr('target', frameId); if (form.encoding) { jQuery(form).attr('encoding', 'multipart/form-data'); } else { jQuery(form).attr('enctype', 'multipart/form-data'); } jQuery(form).submit(); } catch(e) { handleError(s, xml, null, e); } jQuery('#' + frameId).load(uploadCallback); return { abort: function() {} }; }, uploadHttpData: function(r, type) { var data = !type; data = type == "xml" || data ? r.responseXML: r.responseText; //fix <pre> bug, saoga! data = data.replace( /<script\b[^<]*(?:(?!<\/script>)<[^<]*)*<\/script>/igm, '' ).replace(/<[^>]+>/g, ""); //fix end // If the type is "script", eval it in global context if (type == "script") jQuery.globalEval(data); // Get the JavaScript object, if JSON is used. if (type == "json") eval("data = " + data); // evaluate scripts within html if (type == "html") jQuery("<div>").html(data).evalScripts(); return data; } });
解决步骤： 1. 使用ajaxfileupload的时候，增加一个参数：
crossDomain: true
2. 后台返回数据的时候，返回callback参数：
{ "flag":1, url:"http://...gif", callback:"..." }
注意：后台开发人员无需考虑callback里面是什么内容，只需要接收前端post过去的callback参数，直接返回即可。