Docker container can't find path reference - node.js

Question

I'm attempting to run a node.js server with a React frontend using a Docker container on my local Synology NAS. I was able to get the node.js server functioning using this guide.
I then attempted to add the React front end, however I'm getting this error:
ReferenceError: path is not defined ... at /app/lib/app.js:7
app.use(express.static(path.join(__dirname, 'client/build)));
I'm able to run the server locally, so it seems that this would be an issue related to Docker, but I'm not quite sure where to look to resolve the issue.
For reference, the Dockerfile I'm using:
# test using the latest node container
FROM node:latest AS teststep
WORKDIR /app
COPY package.json .
COPY package-lock.json .
COPY lin ./lib
COPY test ./test
RUN npm ci --development
# test
RUN npm test
# build production packages with the latest node container
FROM node:latest AS buildstep
# Copy in package.json, install
# and build all node modules
WORKDIR /app
COPY package.json .
COPY package-lock.json .
RUN npm ci --production
# This is our runtime container that will end up
# running on the device.
FROM node:alpine
WORKDIR /app
# Copy our node_modules into our deployable container context.
COPY --from=buildstep /app/node_modules node_modules
COPY lib ./lib
# Launch our App.
CMD ["node", "lib/app.js"]
App.js:
const express = require('express')
const app = express()
const path = require('path');
const port = 3000
app.use(express.static(path.join(__dirname, 'client/build')));
app.get('/', function(req, res) {
res.sendFile(path.join(__dirname, 'client/build', 'index.html'));
});
app.listen(port, () => console.log(`Example app listening on port ${port}!`))

Answer 1

The problem was fixed by resolving the "lin" typo, then deleting the existing container and executing the run.sh script.