AI solution for JavaScript Quiz on BFE.dev
60. postMessage

The code outputs the following by console.log:

1
5
6
3
2
4

Explanation:

1. console.log(1) is the first statement, so it outputs 1.

2. window.onmessage is set to a callback function, but it doesn't get executed yet.

3. Promise.resolve().then() gets added to the microtasks queue, but the microtasks queue doesn't get executed yet.

4. setTimeout() gets added to the macrotasks queue, which has a minimum delay of 4ms.

5. console.log(5) gets executed, so it outputs 5.

6. window.postMessage('') triggers the window.onmessage callback function, so it outputs 2.

7. console.log(6) gets executed, so it outputs 6.

8. The microtasks queue gets executed. Promise.resolve().then() resolves and logs 3.

9. The macrotasks queue gets executed as well, since it's the only task remaining. setTimeout() logs 4.