Download File Using javascript

 <asp:LinkButton ID="LinkButton1" runat="server" Text=" Download Sample Format"  OnClientClick="DownloadFile('FileName.xlsx')" Style="color: #CC3300"> </asp:LinkButton>

    <script type="text/javascript">
        function DownloadFile(fileName) {
            //Set the File URL.
            var url = "FolderName/" + fileName;

            //Create XMLHTTP Request.
            var req = new XMLHttpRequest();
            req.open("GET", url, true);
            req.responseType = "blob";
            req.onload = function () {
                //Convert the Byte Data to BLOB object.
                var blob = new Blob([req.response], { type: "application/octetstream" });

                //Check the Browser type and download the File.
                var isIE = false || !!document.documentMode;
                if (isIE) {
                    window.navigator.msSaveBlob(blob, fileName);
                } else {
                    var url = window.URL || window.webkitURL;
                    link = url.createObjectURL(blob);
                    var a = document.createElement("a");
                    a.setAttribute("download", fileName);
                    a.setAttribute("href", link);
                    document.body.appendChild(a);
                    a.click();
                    document.body.removeChild(a);
                }
            };
            req.send();
        };
    </script>