How to check NODE_ENV environment variable in Node.JS

You can use process.env.NODE_ENV to check the value of the NODE_ENV environment variable in Node.JS:

if(process.env.NODE_ENV == "development") {
    // TODO your code goes here
}

or

if(process.env.NODE_ENV == "production") {
    // TODO your code goes here
}

Note that by default NODE_ENV is undefined so remember to handle that case appropriately.