If a debug parameter variable is set, output PHP expressions in HTTP headers / Drupal.

my-ajax-debug.drupal.php

<?php


<?php
ini_set( 'display_errors', 1);
error_reporting( E_ALL );

//header( 'Content-Type: text/plain');

function my_test() {
   _ispot_theme_debug(array( 'some data' ));
}

my_test();
echo 'Hello world! ';
flush();
my_test();



// ===================================================================


/** DEBUG: _ispot_theme_debug( $arg1, ... $argN )
*/
function _ispot_theme_debug( $arg_1, /* $... */ $arg_N = null ) {
  static $count;
  $debug = TRUE;
  if ($debug) {
    $count++;
    $caller = _ispot_theme_caller();
    $data = 'X-'. __FUNCTION__ .'-'. sprintf( '%02d', $count ) .': '.
      $caller->fn .'; '. json_encode( func_num_args() > 1 ? func_get_args() : $arg_1 );

    if (headers_sent()): /* ?>
<script>window.console && console.log('<?php echo $data ?>')</script>
    <?php else: */
      header( $data );
    endif;
  }
}

function _ispot_theme_caller( $level = 2 ) {
  $stack = debug_backtrace();
  $result = $stack[ $level ];
  $result[ 'original_file'] = $result[ 'file' ];
  $result[ 'file' ] = basename($result[ 'file' ]);
  $result[ 'fn' ] = $result[ 'function' ];
  return (object) $result;
}


// ===================================================================
// themes/custom/ispot_2013/template.php

/** DEBUG: _ispot_theme_debug( $arg1, ... $argN )
*/
function _ispot_theme_debug( $arg_1, /* $... */ $arg_N = null ) {
  static $count;
  $count++;
  @header( 'X-'. __FUNCTION__ .'-'. sprintf( '%02d', $count ) .': '.
      json_encode( func_num_args() > 1 ? func_get_args() : $arg_1 ));
}


// ===================================================================


/**If a debug parameter or variable is set, output PHP expressions in HTTP headers / Drupal.
 *
 * Inspired by OUVLE/Moodle ouauth, and FirePHP.
 *
 * @copyright 2012-01-31 N.D.Freear.
 * @param mixed $exp... One or more PHP strings and expressions.
 */
function _MY_debug($exp) {
  static $where, $count = 0;
  if (isset($_GET['debug']) || variable_get('debug', NULL)) {
    # $where could be based on __FUNCTION__ or debug_stacktrace().
    if(!$where) $where = str_replace(array('_', '.'), '-', basename(__FILE__));
    header("X-D-$where-".sprintf('%02d', $count).': '.json_encode($exp));

    foreach (func_get_args() as $c => $arg) {
      if($c > 0) _MY_debug($arg); #Recurse.
    }
    $count++;
  }
}
/*Drupal*/ if(!function_exists('variable_get')){function variable_get(){return 1;}}

_MY_debug('Hello world!', array('key'=>'value'), 12345);