<button type="button" class="btn" data-id="1">
<button type="button" class="btn" data-id="2">
<button type="button" class="btn" data-id="3">

<script type="text/javascript">
$(function() {
  $('.btn').on('click', function(){
    console.log($(this).data('id'));
  });
});
</script>

<input type="file" class="file" name="file_1" data-num="1">
<input type="file" class="file" name="file_2" data-num="2">
<input type="file" class="file" name="file_3" data-num="3">

<script type="text/javascript">
$(function() {
  $('.file').on('change', function(){
    console.log($(this).data('num'));
    console.log($(this).val());
  });
});
</script>