upload_lab1.html

<html>
 <title>Secure file upload PHP Web Applications</title>
 <head>
 <script language=javascript>
 function chkFileExtension()
 {
    var str=document.upload.userfile.value;
    var ext=str.substring(str.length,str.length-3);
    if ( ext != "gif")
    {
        alert("File is invalid");
        return false;
    }
    else
    {
        return true;
    };
 }
 </script>
 </head>
 <body>
 <form name="upload" action="upload1.php" method="POST" ENCTYPE="multipart/form-data"  onSubmit="return chkFileExtension()">
 Select the file to upload: <input type="file" name="userfile">
 <input type="submit" name="upload" value="upload">
 </form>
 </body>
 </html>