[WordPress] Approaching client-side Ajax functionality across projects will provide you with a formula that works for many WordPress-based projects.

00-ajax-request.js

var data = {
  action:      'process_file_information',
  file_number: 10
};

$.post( ajaxurl, data, function( response ) {

  /* Typically, check the response before trying to parse it.
   * I'm cutting it down for brevity.
   */
  response = $.parseJSON( response );
  
  // More to come...

});

01-parse-response.js

/**
 * Parses the JSON object to determine if the incoming response
 * is valid.
 *
 * @param  JSON json_response The response from the server.
 */
var parse_response = function( json_response ) {
  
  /* Assume that our response looks something like this:
   * {"MESSAGE":"COMPLETE","FILE_NUMBER":"10"}
   */
  
  switch( json_response.MESSAGE ) {
      
      case "COMPLETE":
        // Handle the 'Complete' functionality here.
        break;
      
    case "INCOMPLETE":
        // Handle the 'Incomplete' functionality here.
        break;
     
    default:
        // You have message that's not part of the protocol.
        break;
      
  }  
}

02-ajax-request.js

var data = {
  action:      'process_file_information',
  file_number: 10
};

$.post( ajaxurl, data, function( response ) {

  /* Typically, check the response before trying to parse it.
   * I'm cutting it down for brevity.
   */
  response = $.parseJSON( response );
  parse_response( response );

});