npm install --save env-helpers
yarn add env-helpers
pnpm add env-helpers 

function envStr(key: string, defaultValue: string): string;
function envStr(key: string, defaultValue?: string): string | undefined;

envStr('FOO'): string | undefined
envStr('FOO', 'Fallback'): string

function envInt(key: string, defaultValue: number, radix?: number = 10): number;
function envInt(key: string, defaultValue?: number, radix?: number = 10): number | undefined;

envInt('FOO'): number | undefined
envInt('FOO', 10, 16): number

function envBool(key: string, defaultValue?: boolean): // boolean;

envBoolean('FOO'): boolean
envBoolean('FOO', false): boolean

function envList(key: string, defaultValue: string[]): string[];
function envList(key: string, defaultValue?: string[]): string[] | [];

envList('FOO'): string[] | []
envList('FOO', ['a','b','c']): string[]

function envJSON<T extends object>(key: string, defaultValue: T): T;
function envJSON<T extends object>(key: string, defaultValue?: T): T | undefined;

envJSON<{ [key: string]: string }>('FOO'): { [key: string]: string } | undefined
envJSON<{ biz: string }>('FOO', { biz: 'baz' }): { biz: string }