export default does not return function but object instead

Question

I created a function that tries to import a script by a given source, tries to call its exported function and processes the returned result.

For the sake of simplicity I minimized the code and simply return the result

const getResult = async function (source: string): Promise<unknown> {
    let resultFunction;

    try {
        resultFunction = await import(source);
    } catch (error) {
        // error handling for failed imports
        throw error;
    }

    if (typeof resultFunction !== 'function') {
        // error handling if not a function
        throw new Error("TODO - not a function");
    }

    const result = await resultFunction();

    return result;
};

export { getResult };

I want to write tests for this function. The first sample file in the test directory is

const syncFn = function () {
    return 'sync';
};

export default syncFn;

Next I added a dummy test

import assert from 'assert/strict';
import { getResult } from '../lib/getResult';
import test from 'node:test';

test('getResult', async t => {
    await t.test('first test', async () => {
        const actualResult = await getResult("../test/samples/syncFn.ts"); // it seems I must use the relative path starting at getResult.ts
    
        assert.equal(actualResult, "sync");
    });
});

Sidenotes:

I'm using Node v18.10.0 with the builtin testrunner. The content of the package.json file is

{
    "scripts": {
        "test": "node --test --require ts-node/register $(find . -name '*Tests.ts')"
    },
    "dependencies": {
        "@types/node": "18.8.0"
    },
    "devDependencies": {
        "ts-node": "10.9.1",
        "typescript": "4.8.4"
    }
}

and the whole repo structure is

When running npm run test the test fails because of

TODO - not a function

When inspecting the type of the imported resultFunction I see that it's an object, although I would expect it to be a function.

Does someone know what's wrong?

Camilo · Accepted Answer · 2022-10-06 15:29:15Z

2

The return value of import() is a promise that resolves to an object.

If you want to get the default exported value you need to:

const { default: resultFunction  } = await import(source);

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import#importing_defaults

answered Oct 6, 2022 at 15:29

Camilo

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