If process.env.NODE_ENV is not explicitly set, it returns undefined instead of development

[WaningJupiter]

Hello,
I search the answer for a while
I found this one : #5212
If I understand this correctly : without process.env.NODE_ENV being set, it will return development by default.
What's odd is in my case, it returns undefined. However, I tested with app.get('env'), it returns development.

I'm using express.js v5.3.0.
To reproduce the issue:

import express from 'express'
import type { Express, Request, Response } from 'express'
...

const app: Express = express()

const PORT = 8000
app.get('/', (req: Request, res: Response) => {
 ...
})
...
app.listen(PORT, (): void => {
  console.log("hello world")
})

const myenv = app.get('env')
console.log('my env:', myenv) // return `my env : development`
console.log(process.env.NODE_ENV) // return `my env : undefined`

export default app

Thanks for your help.

[krzysdz]

process.env.NODE_ENV returns the NODE_ENV environmental variable and if you don't set it it will return undefined. This is something managed by Node.js and your OS. app.get('env') returns the app setting called 'env', which is set to the value of process.env.NODE_ENV or 'development' if that variable does not exist or is empty.

express/lib/application.js

Lines 90 to 96 in a419aa7

	app.defaultConfiguration = function defaultConfiguration() {
	var env = process.env.NODE_ENV || 'development';
	// default settings
	this.enable('x-powered-by');
	this.set('etag', 'weak');
	this.set('env', env);

Express won't override the environmental variable if it is not set, but will set it's own setting using the variable if it is available.

[WaningJupiter]

Thank you for the answer and moving my question to the right place.

I found the note at https://expressjs.com/en/guide/migrating-4/ :

...Use the process.env.NODE_ENV or app.get('env') function to
detect the environment and configure the app accordingly.

I think I misread this into both process.env.NODE_ENV or app.get('env') can detect the environnement and offer developmentas backup value. 😅

[shamil-tp]

process.env.NODE_ENV is undefined because Node.js never sets it automatically it only reads what your operating system or launch script provides.
​app.get('env') returns 'development' because Express uses a fallback default. When Express looks at process.env.NODE_ENV and finds nothing (undefined), it chooses 'development' for you. Express only reads your system's settings; it never modifies them.
​In simple terms:
​process.env.NODE_ENV is your computer's actual setting (currently blank/empty).
​app.get('env') is Express's smart guess when that setting is left blank.