Some function for web page view analysis

monitor.js

// Returns entire web page height
function page_height () {
    return Math.max(
        document.body.scrollHeight, document.documentElement.scrollHeight,
        document.body.offsetHeight, document.documentElement.offsetHeight,
        document.body.clientHeight, document.documentElement.clientHeight
    );
}

// Returns visible web page height
function view_height () {
    return window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
}

// Returns ofsset of the visible web page from the top
function view_offset () {
    return window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop;
}