Example code running without env-var. This is how you might implement env.get(MAX_BATCH_SIZE).required().asIntPositive()

without-env-var.example.js

/**
 * All the assertion code below the line could be replaced with
 * this single line by using env-var
 */
env.get(MAX_BATCH_SIZE).required().asIntPositive()

// -----------------------------------------------

const assert = require('assert');

// Our program requires this var to be set
assert.notEqual(
  process.env.MAX_BATCH_SIZE,
  undefined,
  'MAX_BATCH_SIZE environment variable must be set'
);

// Read the var, and use parseInt to make it a number
const MAX_BATCH_SIZE = parseInt(process.env.MAX_BATCH_SIZE, 10);

// Verify we have a valid number, if not throw
assert(
  typeof MAX_BATCH_SIZE === 'number' && !isNaN(MAX_BATCH_SIZE),
  'MAX_BATCH_SIZE env var must be a valid number'
);

// Verify the number is positive
assert(
  MAX_BATCH_SIZE > 0,
  'MAX_BATCH_SIZE must be a positive number'
);

Here's an example of what I usually do, and recommend others do:

'use strict';

import { get } from 'env-var';

const config = {
  NODE_ENV: get('NODE_ENV').default('dev').asEnum(['dev', 'prod']),
  LOG_LEVEL: get('LOG_LEVEL').asString(),
};

export = config;

This solves your issue if you load it early in program execution (since you centralise reading the variables in one step). Hope it helps.