Slim 3 registers two error handers:

• errorHandler to trap PHP Exceptions
• phpErrorHandler to trap PHP 7 Errors

This means that if you want to override the default error handlers, you need to override both error handlers with your own code.

Each error handler is a callable. The signatures are:

• errorHandler: function ($request, $response, $exception)
• phpErrorHandler: function ($request, $response, $error)

To override a error handler, simply register a new callable with the Container:

$container = $app->getContainer();

$container['errorHandler'] = function ($container) {
    return function ($request, $response, $exception) use ($container) {
        // retrieve logger from $container here and log the error
        $response->getBody()->rewind();
        return $response->withStatus(500)
                        ->withHeader('Content-Type', 'text/html')
                        ->write("Oops, something's gone wrong!");
    };
};

$container['phpErrorHandler'] = function ($container) {
    return function ($request, $response, $error) use ($container) {
        // retrieve logger from $container here and log the error
        $response->getBody()->rewind();
        return $response->withStatus(500)
                        ->withHeader('Content-Type', 'text/html')
                        ->write("Oops, something's gone wrong!");
    };
};

If you don’t want to repeat yourself, you can register the `phpErrorHandler` like this:

$container['phpErrorHandler'] = function ($container) {
    return $container['errorHandler'];
};

Note that you can register any PHP callable, so a class with an __invoke() method also works.

Handling PHP notices

As an aside, Slim 2’s error handler catches PHP notices for you (which can be infuriating or very useful!). Slim 3 doesn’t do this by default, so if you want to catch PHP notices then you need to register your own error handler like this:

set_error_handler(function ($severity, $message, $file, $line) {
    if (!(error_reporting() & $severity)) {
        // This error code is not included in error_reporting, so ignore it
        return;
    }
    throw new ErrorException($message, 0, $severity, $file, $line);
});

That’s all there is to it.

Source: AKRABAT