composer require kartik-v/yii2-widget-datepicker "@dev"
php composer updateAnd all. The project is established. But rejoice not worth it. Set the composer on a hosting is not always happiness. So what is installed globally and you do not have admin rights, he can not allow to create temporary files type .cache, and others. Then you have to Dodge and change the way to store these files and composer.json the config.
php composer.phar update