Detecting scroll to bottom of HTML page

gistfile1.js

document.addEventListener("DOMContentLoaded",
        window.addEventListener("scroll",
            function() {
                var b = document.body
                if (b.clientHeight + b.scrollTop >= b.scrollHeight) {
                    // ...
                }
        })

        if (b.clientHeight >= b.scrollHeight) {
            // ...
        }
    })