I'm setting in scripts: "start": "NODE_ENV=development nodemon dist/Server.js"
then trying to read NODE_ENV in code, both dot and bracket notation return undefined:
I have next configurations: "@types/node": "^8.0.53" "typescript": "^2.6.1" node 8.9.1 installed locally
Doesn't seems like process.env even have NODE_ENV after I console.log it.
console.log(process.env.NODE_ENV);
console.log(process.env["NODE_ENV"]); as suggested here
What's wrong with it ?.

You didn't post how you access the NODE_ENV variable in your code, but this works fine for me:
package.json:
test.js
Result of running
npm test:(I'm using node v7.10.1, but I'd expect this to work on any version)