Is it possible to enable changing a variable at runtime?

[bcanseco]

This could be pretty useful for unit tests:

// source.js
import {NODE_ENV} from '@env';

export const doSomethingBasedOnEnvironment = () => {
  if (NODE_ENV === 'production') {
    // business logic here
    return true;
  } else {
    // business logic here
    return false;
  }
};

// source.spec.js

import {doSomethingBasedOnEnvironment} from '.';
import * as env from '@env';

it('should return true in production', () => {
  env.NODE_ENV = 'production';
  expect(doSomethingBasedOnEnvironment()).toBeTruthy();
});

it('should return false in development', () => {
  env.NODE_ENV = 'development';
  expect(doSomethingBasedOnEnvironment()).toBeFalsy();
});

Maybe a contrived example, but in real-world applications the current alternatives aren't ideal:

• Edit the API only for the tests' sake:

  // source.js
  import {NODE_ENV} from '@env';
  
  export const doSomethingBasedOnEnvironment = (environment = NODE_ENV) => {
    if (environment === 'production') {
      return true;
    } else {
      return false;
    }
  };

• Fall back to exclusively using process.env due to the problem below:

  import {NODE_ENV} from '@env';
  
  process.env.NODE_ENV = 'something-else';
  expect(NODE_ENV).toEqual('something-else'); // throws

[goatandsheep]

what you can do is make a file and call it .env.test. This really isn't the purpose of environment variables.