property scrollHeight

This property returns the total scroll height of the currently loaded document content.

function DumpScrollInfo()
{
    var htmlBox = scene.getBoxById("myHtmlBox");
    if (htmlBox)
    {
        shell.print("Scroll Top: " + htmlBox.scrollTop);
        shell.print("Scroll Left: " + htmlBox.scrollLeft);
        shell.print("Scroll Height: " + htmlBox.scrollHeight);
        shell.print("Scroll Width: " + htmlBox.scrollWidth);
    }
}