api-calls.ts

import { RegionIso, CountryIso } from "./types";

export async function getCountryIsos():Promise<CountryIso[]> {
  return [
    {iso: "US", iso3: "USA", name: "United States"},
    {iso: "CA", iso3: "CAN", name: "Canada"},
    {iso: 'JP', iso3: 'JPN', name: 'Japan'}
  ]
}

export async function getRegionIsos():Promise<RegionIso[]>{
  return [
    {abbr: 'OR', name: 'Oregon', countryIso: 'US'},
    {abbr: 'CA', name: 'California', countryIso: 'US'},
    {abbr: 'BC', name: 'British Columbia', countryIso: 'CA'},
    {abbr: 'YT', name: 'Yukon Territory', countryIso: 'CA'},
    {abbr: 'TK', name: 'Tokyo Prefecture', countryIso: 'JP'}
  ]
}

baseImport.js

const theRealObject = {};
console.log('Base Import Called');
module.exports = {
  theRealObject
}

entrypoint.js

const import1 = require('./import1');
const import2 = require('./import2');

const someObj = {};
const someOtherObj = {};
console.log(someObj === someOtherObj);
console.log(import1.theRealObject === import2.theRealObject);

import1.js

const {theRealObject} = require('./baseImport');
module.exports={theRealObject};

import2.js

const {theRealObject} = require('./baseImport');
module.exports={theRealObject};

jest.config.js

module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
};

package.json

{
  "name": "node-imports",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "jest"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@types/jest": "^24.0.15",
    "@types/react": "^16.8.22",
    "@types/react-dom": "^16.8.4",
    "jest": "^24.8.0",
    "parcel-bundler": "^1.12.3",
    "react": "^16.8.6",
    "react-dom": "^16.8.6",
    "react-hooks-testing-library": "^0.6.0",
    "ts-jest": "^24.0.2",
    "typescript": "^3.5.2"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "jsx": "react",
    "lib": ["dom", "esnext"],
    "types": ["jest"]
  }
}

types.ts

export interface CountryIso{
  iso: string;
  iso3:string;
  name:string;
}
export interface RegionIso {
  abbr:string;
  name:string;
  countryIso: string;
}

useLocationIsos.spec.ts

import { makeLocationIsosHook } from "./useLocationIsos";
import { RegionIso, CountryIso } from "./types";
import {renderHook} from 'react-hooks-testing-library';

async function getCountryIsos():Promise<CountryIso[]> {
  return [
    {iso: "US", iso3: "USA", name: "United States"},
    {iso: "CA", iso3: "CAN", name: "Canada"},
    {iso: 'JP', iso3: 'JPN', name: 'Japan'}
  ]
}

async function getRegionIsos():Promise<RegionIso[]>{
  return [
    {abbr: 'OR', name: 'Oregon', countryIso: 'US'},
    {abbr: 'CA', name: 'California', countryIso: 'US'},
    {abbr: 'BC', name: 'British Columbia', countryIso: 'CA'},
    {abbr: 'YT', name: 'Yukon Territory', countryIso: 'CA'},
    {abbr: 'TK', name: 'Tokyo Prefecture', countryIso: 'JP'}
  ]
}
describe('useLocationIsos', () => {
  it('Starts with base country isos and empty region isos', () => {
    const useLocationIsos = makeLocationIsosHook(getCountryIsos, getRegionIsos)
    const {result} = renderHook(useLocationIsos);
  });
});

useLocationIsos.ts

import { useState, useMemo, useEffect } from "react";
import { CountryIso, RegionIso } from "./types";


export interface LocationIsosHook {
  countryIsos: CountryIso[];
  americanStates: RegionIso[];
  canadianProvinces: RegionIso[];
  allRegions:RegionIso[]
}
// Functional Dependency Injection
export function makeLocationIsosHook(getCountryIsos:() => Promise<CountryIso[]>, getRegionIsos: () => Promise<RegionIso[]>){
  return function useLocationIsos():LocationIsosHook{
    throw "Not Implemented Yet";
    // const [countryIsos, setCountryIsos] = useState<CountryIso[]>([
    //   {iso: "US", iso3: "USA", name: "United States"},
    //   {iso: "CA", iso3: "CAN", name: "Canada"}
    // ]);
  
    // const [americanStates, setAmericanStates] = useState<RegionIso[]>([]);
    // const [canadianProvinces, setCanadianProvinces] = useState<RegionIso[]>([]);
    
    // const allRegions = useMemo<RegionIso[]>(() => {
    //   return [...americanStates, ...canadianProvinces];
    // }, [americanStates, canadianProvinces]);
  
    // useEffect(() => {
    //   getCountryIsos().then(setCountryIsos);
    //   getRegionIsos().then((regionIsos: RegionIso[]) => {
    //     setAmericanStates(regionIsos.filter(ri => ri.countryIso === "US"));
    //     setCanadianProvinces(regionIsos.filter(ri => ri.countryIso === "CA"));
    //   })
    // }, []);
  
    // return {
    //   countryIsos,
    //   americanStates,
    //   canadianProvinces,
    //   allRegions
    // }
  }
}