JavaScript / jQuery: Test if window has focus

How do you test if the browser has focus?

use the hasFocus method of the document. You can find detailed description and an example here: hasFocus method

EDIT: Added fiddle http://jsfiddle.net/Msjyv/3/

HTML

Currently <b id="status">without</b> focus...

JS

function check()
{
    if(document.hasFocus() == lastFocusStatus) return;

    lastFocusStatus = !lastFocusStatus;
    statusEl.innerText = lastFocusStatus ? 'with' : 'without';
}

window.statusEl = document.getElementById('status');
window.lastFocusStatus = document.hasFocus();

check();
setInterval(check, 200);

I haven't tested this in other browsers, but it seems to work in Webkit. I'll let you try IE. :o)

Try it out: http://jsfiddle.net/ScKbk/

After you click to start the interval, change the focus of the browser window to see the result change. Again, tested only in Webkit.

var window_focus;

$(window).focus(function() {
    window_focus = true;
}).blur(function() {
    window_focus = false;
});

$(document).one('click', function() {
    setInterval(function() {
        $('body').append('has focus? ' + window_focus + '<br>');
    }, 1000);
});​

Simple javascript snippet

Event based:

function focuschange(fclass) {
    var elems=['textOut','textFocus'];
    for (var i=0;i<elems.length;i++) {
        document.getElementById(elems[i]).
            setAttribute('class',fclass);
    }
}
window.addEventListener("blur",function(){focuschange('havnt')});
window.addEventListener("focus",function(){focuschange('have')});
focuschange('havnt');

.have                { background:#CFC; }
#textOut.have:after  { content:'';      }
.havnt               { background:#FCC; }
#textOut.havnt:after { content:' not';  }

<span id='textOut'>Have</span><span id='textFocus'> focus</span>

Interval pool based:

setInterval(function() {
    var fclass='havnt';
    if (document.hasFocus()) {
      fclass='have';
    };
    var elems=['textOut','textFocus'];
    for (var i=0;i<elems.length;i++) {
        document.getElementById(elems[i]).
            setAttribute('class',fclass);
    }
},100);

#textOut.have:after  { content:'';     }
#textOut.havnt:after { content:' not'; }
.have  { background:#CFC; }
.havnt { background:#FCC; }

<span id='textOut'>Have</span><span id='textFocus'> focus</span>

HTML:

<button id="clear">clear log</button>
<div id="event"></div>​

Javascript:

$(function(){

    $hasFocus = false;

    $('#clear').bind('click', function() { $('#event').empty(); });

    $(window)
        .bind('focus', function(ev){
            $hasFocus = true;
            $('#event').append('<div>'+(new Date()).getTime()+' focus</div>');
        })
        .bind('blur', function(ev){
            $hasFocus = false;
            $('#event').append('<div>'+(new Date()).getTime()+' blur</div>');
        })
        .trigger('focus');

    setInterval(function() {
        $('#event').append('<div>'+(new Date()).getTime()+' has focus '+($hasFocus ? 'yes' : 'no')+'</div>');
    }, 1000);
});​

test

UPDATE:

I'll fix it, but IE does not work very well

test update