by Marcus Viar on WordPress.org
Log PHP variables and arrays to the web console in your browser via JavaScript's console.log(). No browser extensions required.

If PHP Console Log is working and you have not called do_action( 'php_console_log', 'My String or Array' ); you will see a message similar to this in your browsers web console.
Place the do_action( ‘php_console_log’, ‘My String or Array’ ); function anywhere in your WordPress plugin PHP code. The value(s) you pass into do_action( ‘php_console_log’, ‘My String or Array’ ); will be logged to the web console in your browser.
$my_string = 'My String';
do_action( 'php_console_log', $my_string );
$my_array = array(
'elm 1'
'elm 2',
);
do_action( 'php_console_log', $my_array );
$my_array = array(
'key 1'=>'elm 1',
'key 2'=>'elm 2',
);
do_action( 'php_console_log', $my_array);
$my_array = array(
'My String 1',
'My String 2',
array(
'elm 1',
'elm 2',
),
'My String 3',
array(
'key 1'=>'elm 1',
'key 2'=>'elm 2',
'key 3' => array(
'key 3a' => 'elm 3a',
'key 3b' => 'elm 3b',
),
),
'My String 4'
);
do_action( 'php_console_log', $my_array);