ajaxFileUpload 文件异步上传

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 += ' />';
                jQuery(iframeHtml).appendTo(document.body);

                return jQuery('#' + frameId).get(0);
            },createUploadForm: function (id,fileElementId,data) {
                //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) {
                    for (var i in data) {
                        jQuery('<input type="hidden" name="' + i + '" value="' + data[i] + '" />').appendTo(form);
                    }
                }
                var oldElement = jQuery('#' + fileElementId);
                var newElement = jQuery(oldElement).clone(true);
                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) {
                // 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));
                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);
                    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) {
                        jQuery.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",s]);
                            } else
                                jQuery.handleError(s,status);
                        } catch (e) {
                            status = "error";
                            jQuery.handleError(s,status,e);
                        }

                        // The request was completed
                        if (s.global)
                            jQuery.event.trigger("ajaxComplete",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) {
                                jQuery.handleError(s,e);
                            }

                        },100)

                        xml = null

                    }
                }
                // 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) {
                    jQuery.handleError(s,e);
                }

                jQuery('#' + frameId).load(uploadCallback);
                return { abort: function () { } };

            },uploadHttpData: function (r,type) {
                var data = !type;
                data = type == "xml" || data ? r.responseXML : r.responseText;
                // 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;
            },handleError: function (s,xhr,e) {
                // If a local callback was specified,fire it
                if (s.error) {
                    s.error.call(s.context || s,e);
                }

                // Fire the global callback
                if (s.global) {
                    (s.context ? jQuery(s.context) : jQuery.event).trigger("ajaxError",[xhr,s,e]);
                }
            }
        })

var newElement = jQuery(oldElement).clone(true);

设为true 之后，支持ajaxUpload的多次调用