How to get Next.JS environment variables on client side? - reactjs

Question

I have a Next.Js application that I will deploy with docker. I am passing my environment variables in docker file and docker-compose.yaml. Next version: 12.1.6
Dockerfile
# Install dependencies only when needed
FROM node:16-alpine AS deps
# Check https://github.com/nodejs/docker-node/tree/b4117f9333da4138b03a546ec926ef50a31506c3#nodealpine to understand why libc6-compat might be needed.
RUN apk add --no-cache libc6-compat
WORKDIR /app
COPY package.json yarn.lock ./
RUN yarn install --frozen-lockfile
# If using npm with a `package-lock.json` comment out above and use below instead
# COPY package.json package-lock.json ./
# RUN npm ci
# Rebuild the source code only when needed
FROM node:16-alpine AS builder
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .
# Next.js collects completely anonymous telemetry data about general usage.
# Learn more here: https://nextjs.org/telemetry
# Uncomment the following line in case you want to disable telemetry during the build.
# ENV NEXT_TELEMETRY_DISABLED 1
RUN yarn build
# If using npm comment out above and use below instead
# RUN npm run build
# Production image, copy all the files and run next
FROM node:16-alpine AS runner
WORKDIR /app
ENV NODE_ENV production
ENV NEXT_PUBLIC_BASE_URL example --> I'm stating it here. Example is not my value, it just takes space.
# Uncomment the following line in case you want to disable telemetry during runtime.
# ENV NEXT_TELEMETRY_DISABLED 1
RUN addgroup --system --gid 1001 nodejs
RUN adduser --system --uid 1001 nextjs
# You only need to copy next.config.js if you are NOT using the default configuration
# COPY --from=builder /app/next.config.js ./
COPY --from=builder /app/public ./public
COPY --from=builder /app/package.json ./package.json
# Automatically leverage output traces to reduce image size
# https://nextjs.org/docs/advanced-features/output-file-tracing
COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
USER nextjs
EXPOSE 3000
ENV PORT 3000
CMD ["node", "server.js"]
docker-compose.yaml
version: '3'
services:
frontend:
image: caneral:test-1
ports:
- '3000:3000'
environment:
- NEXT_PUBLIC_BASE_URL=https://example.com/api
I am building with the following command:
docker build -t caneral:test-1 .
Then I run docker-compose:
docker-compose up -d
While I can access the NEXT_PUBLIC_BASE_URL value on the server side, I cannot access it on the client side. It returns undefined. Shouldn't I reach it because I define it as NEXT_PUBLIC? This is stated in the official documents.

Answer 1

How to get environment variables on client side?
Details, you have:
Your .env file. (i'm not sure how docker files will affect logic)
Your next.config.js file
Server-side has access to these 2 files.
Client-side doesn't have access to .env file.
What you can do:
In your next.config.js file you can declare a variable where value is your process.env value.
const baseTrustFactor = process.env.trustFactor
IMPORTANT: do not expose your private info (keys/tokens etc.) to the client-side.
If you need to compare the tokens you can:
Send them from the backend (From NodeAPI or similar)
Make conditions in next.config.js such as:
const baseTrustFactor = process.env.trustFactor == '21' ? true : false