HTML upload FILE
<input type="file" id="fighter2_upload" name="fighter2_upload" size=48>

if ( ! document.getElementById('upload-file').value.match(/.jpe?g$/)) {
   alert('JPEG files only');
}

if((document.form1.upload.value.lastIndexOf(".jpg")==-1) {
   alert("Please upload only .jpg extention file");
   return false;
}