How to enable / disable DEBUG mode

To enable DEBUG mode, please replace the content of the index.php file by:

<?php

// comment out the following two lines when deployed to production
defined('YII_DEBUG') or define('YII_DEBUG', true);
defined('YII_ENV') or define('YII_ENV', 'dev');

require(__DIR__ . '/vendor/autoload.php');
require(__DIR__ . '/vendor/yiisoft/yii2/Yii.php');

$config = require(__DIR__ . '/config/web.php');

(new yii\web\Application($config))->run();

As you can see, we have uncommented two lines.

Then, to disable DEBUG mode (for a production enviroment), just replace the content of the index.php file by:

<?php

// comment out the following two lines when deployed to production
// defined('YII_DEBUG') or define('YII_DEBUG', true);
// defined('YII_ENV') or define('YII_ENV', 'dev');

require(__DIR__ . '/vendor/autoload.php');
require(__DIR__ . '/vendor/yiisoft/yii2/Yii.php');

$config = require(__DIR__ . '/config/web.php');

(new yii\web\Application($config))->run();

That’s all!