自制文件上传JS控件，支持IE、chrome、firefox etc.

 (function() {
     if (window.FileUpload) {
         return;
     }
     window.FileUpload = function (id, url) {
         this.id = id;
         this.autoUpload = true;
         this.url = url;
         this.maxSize = null;
         this.extensions = null;
         this.dropId = null;
     };

     window.FileUpload.prototype.init = function() {
         var obj = this;
         $('#' + this.id).change(function () {
             if (obj.autoUpload) {
                 obj.upload();
             }
         });
         if (this.supportsFormData()) {
             if (this.dropId != null) {
                 var drop = $('#' + this.dropId)[0];
                 drop.addEventListener("dragover", function(e) {
                     e.stopPropagation();
                     e.preventDefault();
                     $('#' + obj.dropId).addClass("dragover");
                 }, false);
                 drop.addEventListener("dragout", function(e) {
                     $('#' + obj.dropId).removeClass("dragover");
                 }, false);
                 drop.addEventListener("drop", function(e) {
                     e.stopPropagation();
                     e.preventDefault();
                     $('#' + obj.dropId).removeClass("dragover");
                     obj._uploadUsingFormData(e.dataTransfer.files[0]);
                 }, false);
             }
         } else {
             if (this.dropId != null) {
                 $('#' + this.dropId).hide();
             }
         }
     };

     FileUpload.prototype.supportsFormData = function() {
         return window.FormData != undefined;
     };

     FileUpload.prototype.upload = function() {
         if (this.supportsFormData()) {
             this._uploadUsingFormData($("#" + this.id)[0].files[0]);
         } else {
             this._uploadUsingFrame();
         }
     };

     FileUpload.prototype._uploadUsingFrame = function() {
         var obj = this;
         var $frame = $('#uploadFrame');
         if ($frame.length == 0) {
             $frame = $('<iframe id="uploadFrame" width="0" height="0" name="uploadFrame" src=""></iframe>');
             $frame.appendTo("body");
             $frame.load(function() {
                 var response = $frame.contents().text();
                 try {
                     var json = $.parseJSON(response);
                     $(obj).trigger("onLoad", json);
                 } catch(ex) {
                     $(obj).trigger("onError", response);
                 }
             });
         }
         var form = $("#" + this.id).closest("form")[0];
         form.target = 'uploadFrame';
         form.submit();
     };

     FileUpload.prototype._uploadUsingFormData = function (file) {
         var obj = this;
         var xhr = new XMLHttpRequest();
         xhr.addEventListener("load", function (e) {
             var json = $.parseJSON(xhr.response);
             $(obj).trigger("onLoad", json);
         }, false);
         xhr.addEventListener("error", function (e) {
             $(obj).trigger("onError", e);
         }, false);
         xhr.upload.addEventListener("progress", function (e) {
             if (e.lengthComputable) {
                 $(obj).trigger("onProgress", e.loaded, e.total);
             }
         }, false);
         xhr.open("POST", obj.url);

         if (obj.maxSize != null&&file.size>obj.maxSize) {
             $(obj).trigger("onMaxSizeError");
             return;
         }
         if (obj.extensions != null) {
             var name = file.name;
             var ext = name.substring(name.lastIndexOf("."), name.length).toLowerCase();
             if (obj.extensions.indexOf(ext) < 0) {
                 $(obj).trigger("onExtensionError");
                 return;
             }
         }
         var formData = new FormData();
         formData.append("files", file);
         xhr.send(formData);
     };

     FileUpload.prototype.onLoad = function(handler) {
         $(this).bind("onLoad", function(sender, args) {
             handler && handler(args);
         });
     };

     FileUpload.prototype.onProgress = function (handler) {
         $(this).bind("onProgress", function(sender, loaded, total) {
             handler && handler(loaded, total);
         });
     };

     FileUpload.prototype.onError = function (handler) {
         $(this).bind("onError", function(sender, error) {
             handler && handler(error);
         });
     };

     FileUpload.prototype.onMaxSizeError = function(handler) {
         $(this).bind("onMaxSizeError", handler);
     };

     FileUpload.prototype.onExtensionError = function (handler) {
         $(this).bind("onExtensionError", handler);
     };
 })();

<form enctype="multipart/form-data" id="ctl01" action="Default.aspx" method="post">