How Do I Use an NPM Configuration File In an Intermediate Container?

When trying to

docker build \
--tag my-app:latest \
.

with the following Dockerfile:

FROM node:9-stretch AS intermediate

ARG NPM_TOKEN

COPY [".npmrc", "./"]

RUN ["chmod", "0600", ".npmrc"]

COPY ["package.json", "./"]

RUN ["npm", "install"]

FROM node:9-stretch

WORKDIR /usr/src/app/

COPY --from=intermediate ["node_modules/.", "./node_modules/."]

COPY ["package.json", "index.js", "./"]

CMD ["node", "index.js"]

And the following .npmrc:

//registry.npmjs.org/:_authToken=${NPM_TOKEN}

I receive the following error during step Step 6/14 : RUN ["npm", "install"] of the intermediate container:

Error: Failed to replace env in config: ${NPM_TOKEN}
    at /usr/local/lib/node_modules/npm/lib/config/core.js:417:13
    at String.replace (<anonymous>)
    at envReplace (/usr/local/lib/node_modules/npm/lib/config/core.js:413:12)
    at parseField (/usr/local/lib/node_modules/npm/lib/config/core.js:391:7)
    at /usr/local/lib/node_modules/npm/lib/config/core.js:334:17
    at Array.forEach (<anonymous>)
    at Conf.add (/usr/local/lib/node_modules/npm/lib/config/core.js:333:23)
    at ConfigChain.addString (/usr/local/lib/node_modules/npm/node_modules/config-chain/index.js:244:8)
    at Conf.<anonymous> (/usr/local/lib/node_modules/npm/lib/config/core.js:321:10)
    at /usr/local/lib/node_modules/npm/node_modules/graceful-fs/graceful-fs.js:78:16
    at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:525:3)
/usr/local/lib/node_modules/npm/lib/npm.js:61
      throw new Error('npm.load() required')
      ^

Error: npm.load() required
    at Object.get (/usr/local/lib/node_modules/npm/lib/npm.js:61:13)
    at process.errorHandler (/usr/local/lib/node_modules/npm/lib/utils/error-handler.js:205:18)
    at process.emit (events.js:180:13)
    at process._fatalException (internal/bootstrap/node.js:391:27)

I also have the following line in my .bashrc for my Bash shell and .zshrc for my Z shell:

export NPM_TOKEN=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

I am adding the node_modules to my Docker Image in this fashion in accordance with the official NPM documentation found here.

You're almost there!

According to the official NPM documentation you linked, all you're missing from your docker build command is the --build-arg option, mentioned here and detailed here.

Your finished command should be:

docker build \
--build-arg NPM_TOKEN=${NPM_TOKEN} \
--tag my-app:latest \
.