[Typescript] CommonJS Interop

From source: https://www.typescript-training.com/course/intermediate-v1/03-modules/

Things can sometimes get a bit tricky when consuming CommonJS modules that do things that are incompatible with the way ES Modules typically work.

Most of the time, you can just convert something like

const fs = require("fs")

into

// namespace import
import * as fs from "fs"

but occasionally, you’ll run into a rare situation where the CJS module you’re importing from, exports a single thing that’s incompatible with this namespace import technique.

Here’s a small example of where the namespace import fails:

While this error message is accurate, you may NOT want to follow the advice it provides in all situations.

If you need to enable the esModuleInterop and allowSyntheticDefaultImports compiler flags in order to allow your types to compile, anyone who depends on your types will also have no choice but to enable them.

Thankfully we have another option here — the use of an older module loading API that imports the code properly, and matches up the type information as well

////////////////////////////////////////////////////////
// @filename: fruits.ts
function createBanana() {
  return { name: "banana", color: "yellow", mass: 183 }
}
 
// equivalent to CJS `module.exports = createBanana`
export = createBanana
////////////////////////////////////////////////////////
// @filename: smoothie.ts
 
import createBanana = require("./fruits")
const banana = createBanana()

import createBanana = require("./fruits")

we have solved this by avoiding the use of an ECMAScript import/export. After all, the code we’re referring to here is not following the ES module spec to begin with

The compiled output of this file will still be what we’re looking for in the CJS world

 

"use strict";
function createBanana() {
    return { name: "banana", color: "yellow", mass: 183 };
}
module.exports = createBanana;
////////////////////////////////////////////////////////
 

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var createBanana = require("./fruits");
var banana = createBanana();