Based on this answer here https://stackoverflow.com/a/22524056/777700 I have set exactly the same configuration options, but it doesn't work.
My (partial) app.js file:
console.log('environment: '+process.env.NODE_ENV);
const config = require('./config/db.json')[process.env.NODE_ENV || "development"];
console.log(config);
My ./config/db.json file:
{
    "development":{
        "host":"localhost",
        "port":"3306",
        "username":"root",
        "password":"",
        "database":"dbname"
    },
    "production":{
        "host":"production-host",
        "port":"3306",
        "username":"user",
        "password":"pwd",
        "database":"dbname"
    }
}
Console.log outputs:
environment: development
undefined
and app crashes. Any idea why? File is there, if I remove the [...] part of require(), it does print out the db.json file, with it, it prints out undefined.
EDIT
I tried to add console.log(typeof config) just after require() to see what I'm getting and I have noticed that if I require('./config/db.json')[process.env.NODE_ENV] I get undefined, but if I require('./config/db.json')["development"] I get back proper object.
Versions:
nodeJS 6.11.4
express 4.16.2
 
     
     
    