Use server-side implementation class console to output in the client console debugging information, counters of time and the results of testing.

Note that the Console only works in the debug mode: define('DEBUG_MODE', true);.

<?php
  \Nemiro\Console::Log('Message without parameters.');
  \Nemiro\Console::Log('Message with %s.', 'parameters');

  \Nemiro\Console::Info('Information message without parameters.');
  \Nemiro\Console::Info('Information message: %s, %s, %s', '123', 'abc', 'xyz');

  \Nemiro\Console::Error('Error message!');
  \Nemiro\Console::Error('Message: %s', 'Error message!');

  \Nemiro\Console::Warning('It works only in debug mode!');
  \Nemiro\Console::Warning('It works only in debug mode: define(\'%s\', %s);', 'DEBUG_MODE', 'true');

  \Nemiro\Console::Assert(function(){
    return false; # false for error
  }, 'Error message');

  \Nemiro\Console::Assert(2 * 2 == 4, '2 * 2 != 4');

  \Nemiro\Console::Time('Test timer');
  sleep(1); # pause 1 sec. only for this test
  \Nemiro\Console::TimeEnd('Test timer');
?>

Click on your browser the key combination Ctrl + Shift + I (for IE is F12), to bring up the console.

console