gistfile1.js

//http://code.google.com/p/vimperator-labs/source/browse/common/content/buffer.js?spec=svna58ba2909452326de623a7a978799a44dcf92150&r=ba0d0f68dea50aa115e0d7f27be19c95f1f6ac54#1058
//1058,1090
    findScrollable: function findScrollable(dir, horizontal) {
        let pos = "scrollTop", size = "clientHeight", max = "scrollHeight", layoutSize = "offsetHeight",
            overflow = "overflowX", border1 = "borderTopWidth", border2 = "borderBottomWidth";
        if (horizontal)
            pos = "scrollLeft", size = "clientWidth", max = "scrollWidth", layoutSize = "offsetWidth",
            overflow = "overflowX", border1 = "borderLeftWidth", border2 = "borderRightWidth";

        function find(elem) {
            for (; elem && elem.parentNode instanceof Element; elem = elem.parentNode) {
                let style = util.computedStyle(elem);
                let borderSize = parseInt(style[border1]) + parseInt(style[border2]);
                let realSize = elem[size];
                // Stupid Gecko eccentricities. May fail for quirks mode documents.
                if (elem[size] + borderSize == elem[max] || elem[size] == 0) // Stupid, fallible heuristic.
                    continue;
                if (style[overflow] == "hidden")
                    realSize += borderSize;
                if (dir < 0 && elem[pos] > 0 || dir > 0 && elem[pos] + realSize < elem[max])
                    break;
            }
            return elem;
        }