Downloading image/text file using 'iframe' and 'Ext.core.DomHelper'

[Supriya Kale]

am using Extjs - 4.1.0 and I want to prompt download window. I used 'iframe'. The window gets displayed only when the file being posted is zip/mp3 but when the file being posted is text/image file, the window doesn't appear. Is there some property to be set to enable download window for text/image/different files? Please find my code below.

var record = item.findParentByType('itemcontextmenu').record;
            Ext.Ajax.request({
                url : ORT.Configuration.DOWNLOAD_GRAPHICS_URI+"&graphics="+record.get('id'),
                success: function (response, opt) {
                
                    result = Ext.decode(response.responseText);
                    try {Ext.destroy(Ext.get('graphicsDownloadIframe'));}catch(e) {}
                    Ext.core.DomHelper.append(document.body, {
                        tag: 'iframe',
                        id:'graphicsDownloadIframe',
                        css: 'display:none;visibility:hidden;height:0px;',
                        src: result.fileName,
                        frameBorder: 0,
                        width: 0,
                        height: 0
                    });
                }    
            });

Thanks in advance.