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in package.json:

"scripts": {
  "start": "set NODE_ENV=dev && node app.js"
 }

in app.js:

console.log(process.env.NODE_ENV) // dev
console.log(process.env.NODE_ENV === 'dev') // false
console.log(process.env.NODE_ENV.length) // 4 (including a space at the end) 

so, this may better:

"start": "set NODE_ENV=dev&& node app.js"

or

console.log(process.env.NODE_ENV.trim() === 'dev') // true

For people using *nix (Linux, OS X, etc.), there's no reason to do it via a second export command, you can chain it as part of the invoking command:

NODE_ENV=development node server.js

Easier, no? :)

We ran into this problem when working with node on Windows.

Rather than requiring anyone who attempts to run the app to set these variables, we provided a fallback within the application.

var environment = process.env.NODE_ENV || 'development';

In a production environment, we would define it per the usual methods (SET/export).

You can use the cross-env npm package. It will take care of trimming the environment variable, and will also make sure it works across different platforms.

In the project root, run:

npm install cross-env

Then in your package.json, under scripts, add:

"start": "cross-env NODE_ENV=dev node your-app-name.js"

Then in your terminal, at the project root, start your app by running:

npm start

The environment variable will then be available in your app as process.env.NODE_ENV, so you could do something like:

if (process.env.NODE_ENV === 'dev') {
  // Your dev-only logic goes here
}

In macOS for those who are using the express version 4.x.x and using the DOTENV plugin, need to use like this:

1. After installing the plugin import like the following in the file where you init the application: require('dotenv').config({path: path.resolve(__dirname+'/.env')});

2. In the root directory create a file '.env' and add the varaiable like:

   NODE_ENV=development or NODE_ENV = development

in package.json we have to config like below (works in Linux and Mac OS)

the important thing is "export NODE_ENV=production" after your build commands below is an example:

  "scripts": {
     "start": "export NODE_ENV=production && npm run build && npm run start-server",
     "dev": "export NODE_ENV=dev && npm run build && npm run start-server",
  } 

• for dev environment, we have to hit "npm run dev" command

• for a production environment, we have to hit "npm run start" command

As early as possible in your application, require and configure dotenv.

require('dotenv').config()

In UBUNTU use:

$ export NODE_ENV=test

It is due to OS

In your package.json, make sure to have your scripts(Where app.js is your main js file to be executed & NODE_ENV is declared in a .env file).Eg:

"scripts": {
    "start": "node app.js",
    "dev": "nodemon server.js",
    "prod": "NODE_ENV=production & nodemon app.js"
  }

For windows

Also set up your .env file variable having NODE_ENV=development

If your .env file is in a folder for eg.config folder make sure to specify in app.js(your main js file)

const dotenv = require('dotenv'); dotenv.config({ path: './config/config.env' });

You can use the dotenv package from npm, here is the link:

Which allows you to place all your configuration in a .env file

install dotenv module ( npm i dotenv --save )

require('dotenv').config() //write inside the file where you will use the variable

console.log(process.env.NODE_ENV) // returns value stored in .env file

If you faced this probem in React, you need react-scripts@0.2.3 and higher. Also for other environment variables than NODE_ENV to work in React, they need to be prefixed with REACT_APP_.

For me, the issue was that I was using the pkg library to turn my app into an executable binary. In that case, the accepted solutions didn't work. However, using the following code solved my problem:

const NODE_ENV = (<any>process).pkg ? 'production' : process.env.NODE_ENV;

I found this solution here on GitHub.

In Electron Js

"scripts": {
    "start": "NODE_ENV=development electron index.js",
},

If you define any function with the name process then that may also cause this issue.

Defining process.env.NODE_ENV in package.json for Windows/Mac/Linux:

Here's what worked for me on my Mac (MacBook Pro 2019, 16 inch, Big Sur):

"scripts": {
    "build": "export NODE_ENV=prod || set NODE_ENV=prod&& npx eslint . && node --experimental-json-modules ./backend/app.js && gulp",
},

Using the export NODE_ENV=prod || set NODE_ENV=prod&& string may work in Windows and Linux but I haven't tested that.

If someone could confirm that would be great.

Unfortunately using the cross-env npm package did NOT work for me at all in my package.json file and I spend a long time on my Mac trying to make this work.

I also faced this issue. I moved .env file to the root folder (not the project folder, a level higher) and it worked out.

Check it. it might help you as well

Must be the first require in app.js

npm install dotenv

require("dotenv").config();