JAVASCRIPT

PROCESS.env

process.env.HELLO

what is process.env.node_env

"NODE_ENV is an environment variable made popular by the 
express web server framework. When a node application is run,
it can check the value of the environment variable and do different
things based on the value. 

NODE_ENV specifically is used (by convention) to state whether 
a particular environment is a production or a development environment.
A common use-case is running additional debugging or logging code 
if running in a development environment."

NODE_ENV

//Before running your app, you can do this in console:

//OS X
export NODE_ENV=production

//Win
SET NODE_ENV=production

//PowerShell
$env:NODE_ENV="production"

//or you can run your app like this:
NODE_ENV=production node app.js

//You can also set it in your js file:
process.env.NODE_ENV = 'production';