Untitled

<html>
<head>
<title>validering</title>
<script>
function Validate(){
    var _validFileExtensions = ["xls","xla","xlb","xlc","xld","xlk","xll","xlm","xlt","xlv","xlsx","xlsm","xlsb","xltm","xlam"];
    var input = document.getElementById("upload");
    if(input.type == "file"){
        var fileName = input.value;
        var ext = fileName.substring(fileName.lastIndexOf('.') +1, fileName.length);
        return _validFileExtensions.lastIndexOf(ext) >= 0;
    }
    return false;
}
(function(){
    window.addEventListener('DOMContentLoaded',load, false);
})();

function load(){
    document.addFile.addEventListener('Submit', Validate, false);
}
</script>
</head>
<body>
<form name="addFile" action="ctrl" method="POST" enctype="multipart/form-data" onSubmit="return Validate(this);">
    <table>
        <tr>
            <td>File: </td>
            <td><input id="upload" type="file" /></td>
            <td><input type="submit" value="Add from file" /></td>
        </tr>
    </table>
</form>
</body>
</html>