flush-promises

What is flush-promises?

The 'flush-promises' npm package is a utility designed to help with testing asynchronous code in JavaScript. It allows you to flush all pending resolved promises, making it easier to test code that relies on asynchronous operations.

What are flush-promises's main functionalities?

Flushing Promises

This feature allows you to flush all pending promises, ensuring that all asynchronous operations have completed. This is particularly useful in testing scenarios where you need to wait for all promises to resolve before making assertions.

const flushPromises = require('flush-promises');

async function asyncFunction() {
  return 'resolved';
}

asyncFunction().then(result => console.log(result));

flushPromises().then(() => {
  console.log('All promises have been flushed');
});

Other packages similar to flush-promises

jest

Jest is a popular testing framework that includes utilities for handling asynchronous code. It provides functions like `waitFor` and `waitForNextUpdate` which can be used to wait for promises to resolve. Compared to 'flush-promises', Jest offers a more comprehensive testing solution but may be overkill if you only need to flush promises.

sinon

Sinon is a library for creating spies, mocks, and stubs in JavaScript. It includes utilities for dealing with asynchronous code, such as `sinon.useFakeTimers` and `sinon.clock.tick`. While Sinon is more focused on mocking and spying, it can also be used to manage asynchronous operations, making it a versatile alternative to 'flush-promises'.

p-settle

The 'p-settle' package is used to settle promises concurrently and get their results. It is useful for handling multiple promises and ensuring they all resolve. While 'p-settle' is more focused on managing multiple promises, 'flush-promises' is specifically designed for flushing all pending promises in a testing context.

README

flush-promises

Flush all pending resolved promise handlers. Useful in tests.

example with async/await

const flushPromises = require('flush-promises');

test('flushPromises', async () => {
  let a;
  let b;

  Promise.resolve().then(() => {
    a = 1;
  }).then(() => {
    b = 2;
  })

  await flushPromises();

  expect(a).toBe(1);
  expect(b).toBe(2);
});

TypeScript

import * as flushPromises from "flush-promises";

test("flushPromises", async () => {
  let a;
  let b;
 
  Promise.resolve().then(() => {
    a = 1;
  }).then(() => {
    b = 2;
  });
 
  await flushPromises();
 
  expect(a).toBe(1);
  expect(b).toBe(2);
});