Alert Interrupt settimeout timing function _javascript Tips

The test found that alert interrupts the settimeout timer, and when the dialog box is closed, settimeout time starts over, not from the interrupt.

For example: SetTimeout to execute a method after 5 minutes, but after waiting 3 minutes, pop-up alert, close alert, settimeout will start to time, and then wait 5 minutes, instead of 2 minutes.

And as long as it is within the same browser window, alert interrupts the settimeout in the other frame, even in a different frame.

Why is it so designed, not understood, because JavaScript is single-threaded?

This is found in IE Explorer, other dialog boxes and pop-up boxes I have not tested.

I hope HTML5 faster and more popular, so the function of multithreading needs can be solved.