为什么 process.env.NODE_ENV 未定义？

Question

I'm trying to follow a tutorial on NodeJS. I don't think I missed anything but whenever I call the process.env.NODE_ENV the only value I get back is undefined . According to my research the default value should be development . How is this value dynamically set and where is it set initially?

Answer 1

process.env is a reference to your environment, so you have to set the variable there.

To set an environment variable in Windows :

SET NODE_ENV=development

on macOS / OS X or Linux :

export NODE_ENV=development

Answer 2

tips

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

Answer 3

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? :)

Answer 4

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).

Answer 5

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
}

Answer 6

In macOS for those who are using the express version 4.xx 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

Answer 7

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

Answer 8

尽早在您的应用程序中要求并配置 dotenv。

require('dotenv').config()

Answer 9

In UBUNTU use:

$ export NODE_ENV=test

Answer 10

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

Answer 11

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' });

Answer 12

You can use the dotenv package from npm, here is the link: https://www.npmjs.com/package/dotenv

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

Answer 13

Must be the first require in app.js

npm install dotenv

require("dotenv").config();

Answer 14

In my case, I have a node app. The way I have structured it is that I have client folder and server folder. I had my .env file inline with these two folder. My server file needs the .env file. It was returning undefined because it did not live inside the server file. It was an oversight.

App
-client
-server
-.env

Instead I moved .env inside server file like so:

App
-client
-server
 |-.env <---here
 |-package.json
 |-and the rest of the server files...

(before this - ofcourse have the dotenv npm package installed and follow its doc)

Answer 15

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_ .

Answer 16

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 solutionhere on GitHub.

Answer 17

In Electron Js

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

Answer 18

如果您使用名称process定义任何函数，那么这也可能导致此问题。

Answer 19

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&& 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.

Answer 20

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

Answer 21

也可以通过代码设置，例如：

process.env.NODE_ENV = 'test';