Steps for importing a CommonJS module with module.exports in Typescript

When working with ES5 code, I encountered an error that I cannot seem to resolve. Despite following the language spec and checking my TypeScript version 1.7.5, I still can't figure out why this error is occurring.

Error TS2349: Cannot invoke an expression whose type lacks a call signature.

a.js (ES5 ambient module with default export)

function myfunc() {
  return "hello";
}
module.exports = myfunc;

a.d.ts

declare module "test" {
    export default function (): string;
}

b.ts

import test = require("test");
const app = test();

b.js (generated ES5):

var test = require("test");
var app = test()

Answer №1

When using module.exports in a CommonJS module, you are exporting a literal value. However, if you use export default, it implies that you are exporting a default property, which may not align with the actual behavior of your JavaScript code.

To properly export in this scenario, you should utilize the syntax export = myfunc:

declare module "test" {
    function myfunc(): string;
    export = myfunc;
}

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