Async module.exports dependency in Node.js

Question

I have two test files in Node.js that depend on each other. The first test runs some async work, and at the end exports an object with a UUID that the second test requires.

test_1.js

'use strict';

# simulate some async work
setTimeout(() => {
    module.exports = {
        id: '83b50527-73a9-4926-8247-e37547f3da6d'
    };
}, 2000);

test_2.js

'use strict';

const testOne = require('./test_1.js');
console.log(testOne);

The problem is since the module.exports is called async in the first test, in test two console.log(testOne) is just an empty object.

How can I make test_2.js wait until test_1.js is finished exporting?

Season · Accepted Answer · 2016-09-29 00:58:46Z

3

Promise to the rescue is one fashion for it.

test_1.js

module.exports = new Promise(resolve => {
  setTimeout(() => resolve({
    id: '83b50527-73a9-4926-8247-e37547f3da6d'
  }), 2000);
});

test_2.js

const testOne = require('./test_1.js');
testOne.then(uuid => console.log(uuid.id));

Carefully bear in mind that the same promise instance is returned each time test_1.js is imported. This effects how the promise instance shall be consumed.

edited Sep 29, 2016 at 0:58

answered Sep 29, 2016 at 0:51

Season

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5 Comments

Toolkit Over a year ago

so even if I comment out testOne.then, setTimeout fires anyway. This doesn't make any sense. And how can I pass parameters anyway?

Season Over a year ago

I would not import a module without consuming it.

Toolkit Over a year ago

and how do i pass parameter? let's say delay time? thaks

Season Over a year ago

Export from test1 a hugher order function instead which returns the promise. In test2, call the function with parameters and get the promise.

Toolkit Over a year ago

you don't need to return promise, you just export async function and await it

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