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AI solution for JavaScript Quiz on
62. MessageChannel

The code outputs:


Here's the breakdown of what's happening:

  • The first console.log(1) is immediately executed and logs 1.

  • A MessageChannel is created and stored in the mc variable.

  • A callback function is assigned to the onmessage event of the mc.port1. This function logs 2.

  • A Promise is created with Promise.resolve(), and a then() method is chain called on it with a callback function that logs 3.

  • A setTimeout() is called with a callback function that logs 4, and a delay of 0ms, so it will be executed as soon as possible after the current task queue has been processed.

  • Another console.log(5) logs 5.

  • A message is sent through mc.port2 with mc.port2.postMessage(''). This will trigger the onmessage callback function registered on mc.port1, which logs 2.

  • Finally, console.log(6) logs 6.

So the overall order of execution is:

  1. console.log(1)
  2. mc
  3. Promise.resolve().then()
  4. setTimeout()
  5. console.log(5)
  6. mc.port2.postMessage('')
  7. console.log(6)
  8. mc.port1.onmessage() (logs 2)
  9. console.log(3)
  10. setTimeout() callback (logs 4)