var discoverScreenSize_availableWidth = -1;
var discoverScreenSize_availableHeight = -1;

function getAvailableWidth() {
    if(discoverScreenSize_availableWidth == -1)
        discoverScreenSize_discoverAvailableScreenSize();
    return discoverScreenSize_availableWidth;
}
function getAvailableHeight() {
    if(discoverScreenSize_availableHeight == -1)
        discoverScreenSize_discoverAvailableScreenSize();
    return discoverScreenSize_availableHeight;
}

function discoverScreenSize_discoverAvailableScreenSize() {
    var div = document.createElement('div');
    with(div.style) {
        width = '1px';
        height = '1px';
        margin = '0px';
    }
    var element = document.createElement('div');
    with(element.style) {
        margin = '0px';
        padding = '0px';
        position = 'absolute';
        top = '0px';
        left = '0px';
        width = '100%';
        height = '100%';
        overflow = 'auto';
    }
    element.appendChild(div);
    document.body.appendChild(element);

    while(element.scrollLeft == 0) {
        div.style.width = discoverScreenSize_increase(div.style.width, 1) + 'px';
        element.scrollLeft = 10000;
    }
    discoverScreenSize_availableWidth = discoverScreenSize_increase(div.style.width, -1);
    div.style.width = 1;

    while(element.scrollTop == 0) {
        if(element.scrollTop == 0)
            div.style.height = discoverScreenSize_increase(div.style.height, 1) + 'px';
        element.scrollTop = 10000;
    }
    discoverScreenSize_availableHeight = discoverScreenSize_increase(div.style.height, -1);
    div.style.height = 1;

    document.body.removeChild(element);
}
function discoverScreenSize_increase(pixels, amount) {
    amount = Math.round(amount);
    return value = parseInt(pixels.replace('px', '')) + amount;
}