document.hasFocus to check window active or not

var window_status=document.hasFocus();

Checking the status of focus

<script language=javascript>
if ( document.hasFocus() ) {
// window is in focus
}else{
// window is NOT in focus
}
</script>

<script language=javascript>
//////////////////
function display_c(){
var refresh=1000; // Refresh rate in milli seconds
mytime=setTimeout('display_msg()',refresh)
}
////////////////////////////
function display_msg() {
if ( document.hasFocus() ) {
document.getElementById('my_msg').style.backgroundColor = "#00f000";	
document.getElementById('my_msg').innerHTML = "This document is in Focus ";
}else{
document.getElementById('my_msg').style.backgroundColor = "#f07814";
document.getElementById('my_msg').innerHTML = "This document is NOT in Focus ";	
}
display_c();
}
//////////////
</script>