var window_id;

function begin_chat() {
    if ( !CheckWindowOpen( 'user_chat_popup' ) ) {
        window_id = window.open( '/__chat.phtml', 'user_chat_popup','location=0,status=0,toolbar=0,menubar=0,directories=0,scrollbars=1,resizable=1,width=550,height=400,top=50,left=50' );
    } else {
        window_id.focus();
    }
}

function CheckWindowOpen(myName) {
    try {
        if( eval( "window." + myName + ".document" ) ) /* check if window exists.*/ { return true; }
    }
    catch(e) {
        return false;/*If not iopen it will throw err*/
    }
}