Javascript-setTimeout / setInterval在函数之前执行倒计时

Question

I have a timer which triggers a function each 3 seconds using setTimeout or setInterval. The point is that I need to execute the countdown before the function instead of execute the function first and then the timer.

This is the code:

var timer;

document.getElementById('myBtn').addEventListener('mousedown', function (){
    timer = setInterval(alert("Ey, release the button!"), 3000);
});

And this should be the order of actions:

1. Click and hold the button.
2. Start the countdown ...3, 2, 1...
3. Trigger the function.

Answer 1

You could trigger another function at the end of the timer. Since you only need to call it once.. You could just use setTimeout

document.getElementById('myBtn').addEventListener('mousedown', function (){
    alert("Ey, release the button!")
    setTimeout(fireMe, 3000);
});

function fireMe() {
    // Boom
}

You might also want to add clearTimeout on mouseup event.

Answer 2

Do something like

var timer;

   document.getElementById('myBtn').addEventListener('mousedown', function (){
     timer = setTimeout(function(){
       alert("Ey, release the button!");
     }, 3000);
});