next.js environment variables are undefined (Next.js 10.0.5)

Question

I am coding a website with Next.js and I tried to add google Tag Manager.
I followed the tutorial on the Next.js Github example but for some reasons I can't access to my environment variables.
It says my variable is undefined.
I created a file .env.local on my project folder (at the same level as components, node_modules, pages, etc)
In this file I created a variable like this (test purpose) :

NEXT_PUBLIC_DB_HOST=localhost

And on my index page I tried this code :

console.log("test ", process.env.NEXT_PUBLIC_DB_HOST);

But in my console I get a "test undefined".
I tried to put my variable into an .env file instead, without success.
What I am doing wrong ?

Answer 1

This envs just works in Server Side. To access this envs in Client Side, you need declare in the next.config.js

This way:

module.exports = {
  reactStrictMode: true,
  env: {
    BASE_URL: process.env.BASE_URL,
  }
}

Answer 2

1. Create .env (all environments), .env.development (development environment), and .env.production (production environment).

2. Add the prefix NEXT_PUBLIC to all of your environment variables.

NEXT_PUBLIC_API_URL=http://localhost:3000/

3. Use with prefix process.env

process.env.NEXT_PUBLIC_API_URL

4. Stop the server and restart it:

npm run dev

5. I hope it works. This solution for latest version of nextJs (above 9)

Answer 3

Restarting the server worked for me.

1. Edit & save .env.local
2. Stop the server and restart it, npm run dev
3. You should get an output on the next line like this:

> [email protected] dev
> next dev

Loaded env from [path]/.env.local

Answer 4

For those using NextJS +9 and looking for environment variables in the browser, you should use the NEXT_PUBLIC_ prefix. Example:

NEXT_PUBLIC_ANALYTICS_ID=123456789

See documentation for reference.

Answer 5

After spending countless hours on this, I found that there is a tiny little paragraph in both the pre and post nextjs 9.4 documentation:

• (Pre-9.4) https://nextjs.org/docs/api-reference/next.config.js/environment-variables (same as this answer)

  Next.js will replace process.env.customKey with 'my-value' at build time.

• (^9.4) https://nextjs.org/docs/basic-features/environment-variables

  In order to keep server-only secrets safe, Next.js replaces process.env.* with the correct values at build time.

Key words being BUILD TIME. This means you must have set these variables when running next build and not (just) at next start to be available for the client side to access these variables.