How to filter input type="file" dialog by specific file type?

Add a custom attribute to <input type="file" file-accept="jpg gif jpeg png bmp"> and read the filenames within javascript that matches the extension provided by the attribute file-accept. This will be kind of bogus, as a text file with any of the above extension will erroneously deteted as image.

<asp:FileUpload ID="FileUploadExcel" ClientIDMode="Static" runat="server" />
<asp:Button ID="btnUpload" ClientIDMode="Static" runat="server" Text="Upload Excel File" />

.

$('#btnUpload').click(function () {
    var uploadpath = $('#FileUploadExcel').val();
    var fileExtension = uploadpath.substring(uploadpath.lastIndexOf(".") + 1, uploadpath.length);

    if ($('#FileUploadExcel').val().length == 0) {
        // write error message
        return false;
    }

    if (fileExtension == "xls" || fileExtension == "xlsx") {
        //write code for success
    }
    else {
        //error code - select only excel files
        return false;
    }

});

See http://www.w3schools.com/tags/att_input_accept.asp:

The accept attribute is supported in all major browsers, except Internet Explorer and Safari. Definition and Usage

The accept attribute specifies the types of files that the server accepts (that can be submitted through a file upload).

Note: The accept attribute can only be used with <input type="file">.

Tip: Do not use this attribute as a validation tool. File uploads should be validated on the server.

Syntax <input accept="audio/*|video/*|image/*|MIME_type" />

Tip: To specify more than one value, separate the values with a comma (e.g. <input accept="audio/*,video/*,image/*" />.

This will give the correct (custom) filter when the file dialog is showing:

<input type="file" accept=".jpg, .png, .jpeg, .gif, .bmp, .tif, .tiff|image/*">