Question

want to get a validation script to validate the file upload box onsubmit.

check the extension of the file and validate accordingly to the extension of file loaded

Answer 1

Check here: http://jsfiddle.net/uh2Gn/

HTML:

<form method="post" enctype="" onsubmit="return validate()">
    <input type="file" id="file" />
    <input type="submit" />
</form>

JavaScript:

function validate() {
    var filename=document.getElementById('file').value;
    var extension=filename.substr(filename.lastIndexOf('.')+1).toLowerCase();
    //alert(extension);
    if(extension=='jpg' || extension=='gif') {
        return true;
    } else {
        alert('Not Allowed Extension!');
        return false;
    }
}

Keep in mind that this is only for user convenience, that he doesn’t go theu a long submit process to get an error at the server, cuz for sure you must implement a check at server-side.