WordPress docker image. How to add NPM?

I try create my WordPress/Docker starter. I have docker-compose.yml file and it's works.

version: '2'

services:
   db:
     image: mysql:5.7
     volumes:
       - db_data:/var/lib/mysql
     restart: always
     environment:
       MYSQL_ROOT_PASSWORD: wordpress
       MYSQL_DATABASE: wordpress
       MYSQL_USER: wordpress
       MYSQL_PASSWORD: wordpress

   wordpress:
     depends_on:
       - db
     image: wordpress:latest
     ports:
       - "8000:80"
     restart: always
     environment:
       WORDPRESS_DB_HOST: db:3306
       WORDPRESS_DB_PASSWORD: wordpress
     volumes:
      - .app/wp-content/themes:/var/www/html/wp-content/themes
volumes:
    db_data:

But in docker bash i received npm command not found. Where can i add node install?

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