Vtyjkyuk

I want to put if-else condition whether it is front or backend.

How can I do that?

With objectManager

$objectManager = MagentoFrameworkAppObjectManager::getInstance();
$state = $objectManager->get('MagentoFrameworkAppState');
echo $state->getAreaCode(); //frontend or adminhtml

With Dependency Injection

protected $_state;

public function __construct (
 MagentoFrameworkAppState $state
) 
 $this->_state = $state;


public function getArea()

 return $this->_state->getAreaCode();

Note: As per magento2 coding standards don't use object manager instance directly in files

Use below code

$objectmanager = MagentoFrameworkAppObjectManager::getInstance();
$state = $objectmanager->get('MagentoFrameworkAppState');
if($state->getAreaCode() == 'frontend')
 //frontend
else
 //backend

Try code below for check if you are in admin area

function df_is_admin($store = null) 
 /** @var MagentoFrameworkObjectManagerInterface $om */
 $om = MagentoFrameworkAppObjectManager::getInstance();
 /** @var MagentoFrameworkAppState $state */
 $state = $om->get('MagentoFrameworkAppState');
 return 'adminhtml' === $state->getAreaCode();

People have answered the question already.
I am just making it better.

const AREA_CODE = MagentoFrameworkAppArea::AREA_ADMINHTML;

private $_state;

public function __construct (
 MagentoFrameworkAppState $state
) 
 $this->_state = $state;


public function isAdmin()

 $areaCode = $this->_state->getAreaCode();

 if ($areaCode == self::AREA_CODE) 
 return true;
 else 
 return false;