How to get response as json format(application/json) in yii?

For Yii 1:

Create this function in your (base) Controller:

/**
 * Return data to browser as JSON and end application.
 * @param array $data
 */
protected function renderJSON($data)
{
    header('Content-type: application/json');
    echo CJSON::encode($data);

    foreach (Yii::app()->log->routes as $route) {
        if($route instanceof CWebLogRoute) {
            $route->enabled = false; // disable any weblogroutes
        }
    }
    Yii::app()->end();
}

Then simply call at the end of your action:

$this->renderJSON($yourData);

For Yii 2:

Yii 2 has this functionality built-in, use the following code at the end of your controller action:

Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
return $data;

$this->layout=false;
header('Content-type: application/json');
echo CJavaScript::jsonEncode($arr);
Yii::app()->end(); 

For Yii2 inside a controller:

public function actionSomeAjax() {
    $returnData = ['someData' => 'I am data', 'someAnotherData' => 'I am another data'];

    $response = Yii::$app->response;
    $response->format = \yii\web\Response::FORMAT_JSON;
    $response->data = $returnData;

    return $response;
}