How to check javascript errors

variant 1)

$has_js_errors = $session->execute(array('script' => 'return $("body").attr("JSError") != undefined', 'args' => array()));

variant 2)

--- a/php-webdriver/PHPWebDriver/WebDriverSession.php
+++ b/php-webdriver/PHPWebDriver/WebDriverSession.php
@@ -46,6 +46,7 @@ class PHPWebDriver_WebDriverSession extends PHPWebDriver_WebDriverContainer {
       'doubleclick' => 'POST',
       'location' => array('GET', 'POST'),
       'file' => 'POST',
+      'log' => 'POST',
     );
   }

....

$session = $web_driver->session('chrome', array('loggingPrefs'=>array('browser'=>'ALL')));

.....

$has_js_errors_in_console = $session->log(array('type'=>'browser'));
$has_js_errors_in_console = array_filter($log, function($v) {return !in_array($v['level'], array('INFO','WARNING'));});