How to identify if a key is down on hover?

Question

I would like to show one div only when another div is hovered and the Space Bar is down. I tried to use keyCode and which properties of the event, but none of them worked. Though, I could create an example for CTRL key pressed rather than the Space Bar, as you can see also here.

How should I change the code so it will work with Space Bar (or any other key) down?

HTML:

<div class='a'></div>
<div class='b'></div>

CSS:

body {
    position: relative;
}
div {
    width: 100px;
    height: 100px;
    position: absolute;
}
.a {
    background: #777;
    left: 50px;
    top: 30px;
}
.b {
    display: none;
    background: #000;
    left: 250px;
    top: 100px;
}

JS:

$(function() {
    $('div').hover(function(e) {
        if (e.ctrlKey) {
            $('.b').show();
        }
    }, function() {
        if ($('.b').is(':visible')) $('.b').hide();
    });
});

Answer 1

You can make use of the fact that .hover() binds 2 handlers. One for mouseenter and one for mouseleave.

Bind a .keydown() on mouseenter and simply .unbind() it on mouseleave:

$(function() {

      // Define the mouseenter and mouseleave handlers with hover
    $("div.a").hover(function() {

          // Show other div if a key is pressed.
          // You can of course check for on particular key.
        $(document).keydown(function() {
            $("div.b").show();
        });

    }, function() {

         // unbind the keydown handler on mouseleave
       $(document).unbind("keydown");

       $("div.b").hide();
    });
});​

jsFiddle example

An important note is that .hover() will work even if the window hasn't been focused, but .keydown() will only work if the window is in focus.