สอบถามหน่อยคะ Extjs จะสร้างปุ่ม upload file เฉพาะ .txt เท่านั้น

<script type="text/javascript">
$(document).ready(function(){
$('INPUT[type="file"]').change(function () {
    var ext = this.value.match(/\.(.+)$/)[1];
    if(ext != 'txt') {
            alert('This is not an allowed file type.');
            this.value = '';
    }
});
});
</script>

<input type='file' />

 var fbutton = new Ext.ux.form.FileUploadField({
	        renderTo: 'uploadBtn',
	        buttonOnly: true,
	        listeners: {
	            'fileselected': function(fb, v){
	                var el = Ext.fly('uploadBtn-msg');
	                el.update('<b>Selected:</b> '+v);
	                if(!el.isVisible()){
	                    el.slideIn('t', {
	                        duration: .2,
	                        easing: 'easeIn',
	                        callback: function(){
	                            el.highlight();
	                        }
	                    });
	                }else{
	                    el.highlight();
	                }
	            }
	        }
	    });

{
        xtype:'filefield',
        reset: function () {  
          var me = this,                                                                
            clear = me.clearOnSubmit;
         if (me.rendered) {   
            me.button.reset(clear);
            me.fileInputEl = me.button.fileInputEl;
            me.fileInputEl.set({
               accept: 'audio/*'    
            });
            if (clear) {
               me.inputEl.dom.value = '';
            }
            me.callParent();
        }},
        listeners:{
           afterrender:function(cmp){
              cmp.fileInputEl.set({
                  accept:'audio/*'
              });
           }
        }
}