Promise execute order is not same as browser and Node.js

[zizifn]

Background

Promise queue or Microtask queue will exhausted in the end of each event callback.

Code

const xhr = new XMLHttpRequest();
xhr.open('GET', 'https://jsonplaceholder.typicode.com/todos/1', true);
xhr.addEventListener("readystatechange", () => {
    if (xhr.readyState === 4 && xhr.status === 200) {
        console.log('readystatechange1', JSON.parse(xhr.responseText));
        Promise.resolve("readystatechange1->promise1").then(console.log);
    }
});
xhr.addEventListener("readystatechange", () => {
    if (xhr.readyState === 4 && xhr.status === 200) {
        console.log('readystatechange2', JSON.parse(xhr.responseText));
        Promise.resolve("readystatechange2->promise2").then(console.log);
    }
});
xhr.send();

Browser

readystatechange1 {userId: 1, id: 1, title: 'delectus aut autem', completed: false}
readystatechange1->promise1
readystatechange2 {userId: 1, id: 1, title: 'delectus aut autem', completed: false}
readystatechange2->promise2

txiki.js

readystatechange1 {
 userId: 1,
  id: 1,
  title: 'delectus aut autem',
  completed: false
}
readystatechange2 {
 userId: 1,
  id: 1,
  title: 'delectus aut autem',
  completed: false
}
readystatechange1->promise1
readystatechange2->promise2

I'm not very familiar with txiki.js or libuv, but I think it might be because txiki.js executes promise jobs in the uv_check phase, meaning promise jobs run in each loop iteration rather than after each event callback.

[saghul]

A tricky one! Thanks for the report!