javascriptのdrag&dropで、drop出来るファイル形式を指定する方法が知りたいです

ソースは下記の通りで、drop出来るファイル形式に指定はありません。
つまり、どんなファイルでもdrop出来るのが現状です。
これを、drop出来るファイル形式を指定をしたいのですが、方法が分かりません。
例えばtextファイルのみをdrop出来るようにしたいです。

・ソース

lang
1<html>
2<head>
3<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.min.js"></script>
4<style>
5#dragandrophandler
6{
7border:2px dotted #0B85A1;
8width:400px;
9color:#92AAB0;
10text-align:left;vertical-align:middle;
11padding:10px 10px 10 10px;
12margin-bottom:10px;
13font-size:200%;
14}
15.progressBar {
16    width: 200px;
17    height: 22px;
18    border: 1px solid #ddd;
19    border-radius: 5px;
20    overflow: hidden;
21    display:inline-block;
22    margin:0px 10px 5px 5px;
23    vertical-align:top;
24}
25  
26.progressBar div {
27    height: 100%;
28    color: #fff;
29    text-align: right;
30    line-height: 22px; /* same as #progressBar height if we want text middle aligned */
31    width: 0;
32    background-color: #0ba1b5; border-radius: 3px;
33}
34.statusbar
35{
36    border-top:1px solid #A9CCD1;
37    min-height:25px;
38    width:700px;
39    padding:10px 10px 0px 10px;
40    vertical-align:top;
41}
42.statusbar:nth-child(odd){
43    background:#EBEFF0;
44}
45.filename
46{
47display:inline-block;
48vertical-align:top;
49width:250px;
50}
51.filesize
52{
53display:inline-block;
54vertical-align:top;
55color:#30693D;
56width:100px;
57margin-left:10px;
58margin-right:5px;
59}
60.abort{
61    background-color:#A8352F;
62    -moz-border-radius:4px;
63    -webkit-border-radius:4px;
64    border-radius:4px;display:inline-block;
65    color:#fff;
66    font-family:arial;font-size:13px;font-weight:normal;
67    padding:4px 15px;
68    cursor:pointer;
69    vertical-align:top
70    }
71</style>
72</head>
73  
74<body>
75<div id="dragandrophandler">ここにドロップしてください。</div>
76<br><br>
77<div id="status1"></div>
78<script>
79function sendFileToServer(formData,status)
80{
81    var uploadURL ="http://hayageek.com/examples/jquery/drag-drop-file-upload/upload.php"; //Upload URL
82    var extraData ={}; //Extra Data.
83    var jqXHR=$.ajax({
84            xhr: function() {
85            var xhrobj = $.ajaxSettings.xhr();
86            if (xhrobj.upload) {
87                    xhrobj.upload.addEventListener('progress', function(event) {
88                        var percent = 0;
89                        var position = event.loaded || event.position;
90                        var total = event.total;
91                        if (event.lengthComputable) {
92                            percent = Math.ceil(position / total * 100);
93                        }
94                        //Set progress
95                        status.setProgress(percent);
96                    }, false);
97                }
98            return xhrobj;
99        },
100    url: uploadURL,
101    type: "POST",
102    contentType:false,
103    processData: false,
104        cache: false,
105        data: formData,
106        success: function(data){
107            status.setProgress(100);
108  
109            $("#status1").append("File upload Done<br>");        
110        }
111    });
112  
113    status.setAbort(jqXHR);
114}
115  
116var rowCount=0;
117function createStatusbar(obj)
118{
119     rowCount++;
120     var row="odd";
121     if(rowCount %2 ==0) row ="even";
122     this.statusbar = $("<div class='statusbar "+row+"'></div>");
123     this.filename = $("<div class='filename'></div>").appendTo(this.statusbar);
124     this.size = $("<div class='filesize'></div>").appendTo(this.statusbar);
125     this.progressBar = $("<div class='progressBar'><div></div></div>").appendTo(this.statusbar);
126     this.abort = $("<div class='abort'>Abort</div>").appendTo(this.statusbar);
127     obj.after(this.statusbar);
128  
129    this.setFileNameSize = function(name,size)
130    {
131        var sizeStr="";
132        var sizeKB = size/1024;
133        if(parseInt(sizeKB) > 1024)
134        {
135            var sizeMB = sizeKB/1024;
136            sizeStr = sizeMB.toFixed(2)+" MB";
137        }
138        else
139        {
140            sizeStr = sizeKB.toFixed(2)+" KB";
141        }
142  
143        this.filename.html(name);
144        this.size.html(sizeStr);
145    }
146    this.setProgress = function(progress)
147    {      
148        var progressBarWidth =progress*this.progressBar.width()/ 100; 
149        this.progressBar.find('div').animate({ width: progressBarWidth }, 10).html(progress + "% ");
150        if(parseInt(progress) >= 100)
151        {
152            this.abort.hide();
153        }
154    }
155    this.setAbort = function(jqxhr)
156    {
157        var sb = this.statusbar;
158        this.abort.click(function()
159        {
160            jqxhr.abort();
161            sb.hide();
162        });
163    }
164}
165function handleFileUpload(files,obj)
166{
167   for (var i = 0; i < files.length; i++)
168   {
169        var fd = new FormData();
170        fd.append('file', files[i]);
171  
172        var status = new createStatusbar(obj); //Using this we can set progress.
173        status.setFileNameSize(files[i].name,files[i].size);
174        sendFileToServer(fd,status);
175  
176   }
177}
178$(document).ready(function()
179{
180var obj = $("#dragandrophandler");
181obj.on('dragenter', function (e)
182{
183    e.stopPropagation();
184    e.preventDefault();
185    $(this).css('border', '2px solid #0B85A1');
186});
187obj.on('dragover', function (e)
188{
189     e.stopPropagation();
190     e.preventDefault();
191});
192obj.on('drop', function (e)
193{
194  
195     $(this).css('border', '2px dotted #0B85A1');
196     e.preventDefault();
197     var files = e.originalEvent.dataTransfer.files;
198  
199     //We need to send dropped files to Server
200     handleFileUpload(files,obj);
201});
202$(document).on('dragenter', function (e)
203{
204    e.stopPropagation();
205    e.preventDefault();
206});
207$(document).on('dragover', function (e)
208{
209  e.stopPropagation();
210  e.preventDefault();
211  obj.css('border', '2px dotted #0B85A1');
212});
213$(document).on('drop', function (e)
214{
215    e.stopPropagation();
216    e.preventDefault();
217});
218  
219});
220</script>
221</body>
222</html>