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

user_11713557 0
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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 ?

next.js environment-variables undefined javascript
8 Answers

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,
  }
}
user_112926780

  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/

  1. Use with prefix process.env

process.env.NEXT_PUBLIC_API_URL

  1. Stop the server and restart it:

npm run dev

  1. I hope it works. This solution for latest version of nextJs (above 9)
user_129102980

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:
> klout@0.1.0 dev
> next dev

Loaded env from [path]/.env.local
user_147011550

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.

user_75565510

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:

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.

user_120702970

This is my next.config.js file.

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  env: {
    BASE_URL: process.env.NEXT_PUBLIC_SITE_URL,
  },
};

module.exports = nextConfig;

Restart the server and it worked fine. using Nextjs 12.1.0 with typescript

user_168842330

In my case, Im pasting REACT_APP_API_URL instead of NEXT_PUBLIC_API_URL.

user_78163090

Adding with the most recent version of the documentation on this, v12+.

Using the next.config.js file you can specify server and client variables:

module.exports = {
  serverRuntimeConfig: {
    // Will only be available on the server side
    mySecret: 'secret',
    secondSecret: process.env.SECOND_SECRET, // Pass through env variables
  },
  publicRuntimeConfig: {
    // Will be available on both server and client
    staticFolder: '/static',
  },
}

You can still use an env.local file, and pass the variable in to the next.config.js file. For example:

 publicRuntimeConfig: {
   DB_URL: process.env.DB_URL
 }

And then you can access the variable like this:

import getConfig from 'next/config';
const { publicRuntimeConfig } = getConfig();
publicRuntimeConfig.DB_URL;
user_51004400
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