Environment Variables in Next.js: The Undefined Dilemma

In this NextJs tutorial, w will discuss the very common issues with getting the environs values giving undefined errors. With the help of a sample use case, we will dive into more details on how to set and get Environment values in a NextJS application. There is a number of tools, languages, and frameworks in…


min read

In this NextJs tutorial, w will discuss the very common issues with getting the environs values giving undefined errors. With the help of a sample use case, we will dive into more details on how to set and get Environment values in a NextJS application.

There is a number of tools, languages, and frameworks in the world of web development, and each of them has its unique set of features and capabilities.  NextJS is gaining a lot of attention as a JavaScript framework as one of the popular choices to create front-end apps with server-side capabilities. However, a common hurdle that developers often face is the issue of undefined environment variables in Next.js.

This guide will dig deeper into this concern and enlighten readers about the complications of environment variables in Next.js, and more specifically, how to solve the undefined variable issues. Whether you’re a seasoned Next.js developer or a beginner, understanding this issue can significantly improve your development workflow.


What are Environment Variables?

Before we delve into the heart of the matter, it’s essential to appreciate the role environment variables play. Environment variables, in essence, allow developers to inject configuration settings into their applications.

These variables are crucial for maintaining the security and flexibility of your application, as they enable you to change configurations without modifying the actual code.


The Undefined Variable Problem

Despite the importance of environment variables, developers often encounter a problem – their Next.js environment variables remain undefined. This can lead to application errors, security breaches, and, in the worst cases, a complete application failure. Hence, understanding the cause of this problem and how to fix it is of utmost importance for Next.js developers.


Next.js Environment Variables

Before we delve into the solution, it’s important to understand what Next.js environment variables are and why they might become undefined in your application.

Environment variables in Next.js are specific variables that you can set in your application environment. They allow you to manage sensitive information, such as API keys and database passwords, without exposing them in your code. These variables are defined in a .env file in the root of your Next.js project.


Why do we face Environment Variables Undefined?

The reason Next.js environment variables may be undefined can vary, but it often comes down to a few common issues. Perhaps the most frequent issue is improper naming or misplacement of the .env file. Other reasons might include forgetting to prefix the variable names with NEXT_PUBLIC_ for client-side access or not reloading the Next.js server after defining or updating the variables.


Fixing the Undefined Environment Variables Issue in Next.js

Now that we understand the problem, let’s go through the steps to resolve the undefined environment variables issue in Next.js.


Step 1: Understanding .env File

In Next.js, environment variables are stored in a file named .env located in the root directory of your project. This file is essential for storing sensitive information that should not be exposed within your codebase.


Step 2: Defining Environment Variables

Open the .env file and define your environment variables using the following format:



For example:


Remember to save the file after defining the variables.


Step 3: Accessing Environment Variables in Your Code

Once your environment variables are defined, you can access them in your Next.js code. However, the method for accessing these variables differs depending on whether you are working with server-side or client-side code.


Accessing Environment Variables in Server-side Code

To access environment variables in server-side code, simply use process.env.VARIABLE_NAME. For example:

const apiKey = process.env.API_KEY;

Here’s an example of a sample server.js file:

// Import necessary modules
const express = require('express');
const next = require('next');

// Define the port and dev variables
const port = parseInt(process.env.PORT, 10) || 3000;
const dev = process.env.NODE_ENV !== 'production';

// Set up the Next.js app
const app = next({ dev });
const handle = app.getRequestHandler();

// Define your environment variable
const apiKey = process.env.API_KEY;

// Start the app
app.prepare().then(() => {
  const server = express();

  server.get('/api/data', (req, res) => {
    // Use your environment variable here
    res.send(`Your API Key is ${apiKey}`);

  server.all('*', (req, res) => {
    return handle(req, res);

  server.listen(port, (err) => {
    if (err) throw err;
    console.log(`> Ready on http://localhost:${port}`);

In the above code, we’re using the API_KEY environment variable in a server-side route.


Accessing Environment Variables in Client-side Code

For client-side code, you must prefix your variable names with NEXT_PUBLIC_ in the .env file. For example:



Then, in your client-side code, access the variable using process.env.NEXT_PUBLIC_VARIABLE_NAME. For example:

const apiKey = process.env.NEXT_PUBLIC_API_KEY;

Let’s have a look at the complete example file with env variable usage:

import React from 'react';

const HomePage = () => {
    const apiKey = process.env.NEXT_PUBLIC_API_KEY;

    return (
            <h1>Welcome to the Home Page</h1>
            <p>This is your API Key: {apiKey}</p>

export default HomePage;


Step 4: Deploying Your Next.js Application

When deploying your Next.js application, ensure that the environment variables are properly set in your production environment. The process may vary depending on the hosting platform, but generally, you need to add the environment variables within your deployment settings.


Best Practices for Managing Environment Variables in Next.js

To further ensure that your Next.js environment variables remain secure and functional, consider these best practices:

  1. Never commit your .env file to version control systems like Git. Add the file to your .gitignore to prevent accidental exposure.
  2. Use separate environment variable files (.env.local, .env.development, .env.production) to manage different environment configurations.
  3. Regularly audit your environment variables to ensure their validity and security.



Understanding and properly managing environment variables in Next.js is vital to ensuring the security and flexibility of your applications. By following the steps and best practices outlined in this article, you can effectively troubleshoot and resolve the undefined variable issue, improving your overall development experience in Next.js.

Leave a Reply

Your email address will not be published. Required fields are marked *