Sometimes we need to find the size of a file at the time of uploading to prevent the file that is greater than a particular size. We can achieve this by handling "change" event of a input-file.

Examlpe: Suppose I want to upload a file less than 3 MB.

<input type="file" name="uploadFile" id="uploadFile" class="upload" title="Choose a file to upload"> 
<span id="fileName_error"></span>


<script>
$('#uploadFile').bind('change', function() {
              handleUpload();
          });

function handleUpload(){

          if($('#uploadFile').val() !='')
          {
             //Get size of file
             var size = $('#uploadFile')[0].files[0].size/1024/1024;
             if(size > 3)
             {
                $('#fileName_error').text('Please upload the file less than 3MB.');
                return false;
             }
            $('#fileName_error').text('');
                return true;
          }
      }

</script>

Hope this will help you :)