Keyup not firing when keydown opens an alert

Question

I have two event handlers, one for keydown and one for keyup. The keydown event handler triggers an alert message, but this prevents the keyup event from firing.

You can see a very simple example here: http://jsfiddle.net/boblauer/jaGwT/ When the keydown opens an alert, the keyup is not fired, but when an alert is not opened, the keyup is fired. Here's the code from the jsfiddle:

var i = 0;
window.addEventListener('keydown', function(e) {
    if (i++ % 2) alert('down');
    console.log('down');
});

window.addEventListener('keyup', function(e) {
    alert('up');
    console.log('up');
});

I have a library that supports listening to multiple key combinations (such as 'd + f'), so when a key is pressed, I need to add it to a list of keys that are currently pressed, and when a key is released, I need to remove it from said list. The problem I'm running to is, if I want an alert to show when d + f are pressed at the same time, my code to remove those keys from the 'currently pressed' list never fires, because my keyup handler is never called.

I can't think of a good work around to this problem. Any ideas?

Conduction

That's because alert() blocks - you shouldn't really design your site around using alert()... maybe roll-your-own or use some kind of dialog. – Loper

It also happens in other situations, such as tabbing onto a hyperlink and then hitting enter to open the link. When that happens, the enter's keyup event is not fired. – Conduction

Answer 1

The alert prevents the event from happening. What you could do instead is trigger this function manually, because it happens anyways.

var keyupfunction = function(e){
    alert('up');
    console.log('up');
}

window.addEventListener('keyup', keyupfunction);

window.addEventListener('keydown', function(e) {
    if (i++ % 2) alert('down');
    console.log('down');
    keyupfunction(e);
});

But really, you shouldn't be using alerts. It prevents these events, but who knows what else it might break. Use something custom instead.

Ovolo

The keyup doesn't necessarily follow the keydown event. For example, I can press and hold ctrl, and then press another key without letting up on ctrl. – Conduction

@BobLauer exactly, but in case of alert, there is no other way around it – Ovolo

Thank you, I never would have guessed that the alert was the problem. – Bucaramanga