how to Configure EBS to run npm install

I have node.js application I want to deploy to ebs, however I have two package.jsons for the client and the server. My Idea is that I want server to simply serve the built version of the client.

client
|-package.json
server
|-package.json

I was having a hard time finding in the docs if there was a way to configure the npm install command so it would first run the two installs in each sub directory.

I have nodecommand.config that will start the server ie:

option_settings:
  aws:elasticbeanstalk:container:nodejs:
    NodeCommand: "(cd server && npm run start-prod)"

is there a way to do this for the install as well?