On Scroll handler

var OnScroll = (function () {
    function OnScroll(config) {
        if (!config) {
            config = {}
        }
        this.listeners = [];
        this.timeout = config.timeout || 300;

        var handler = _scrollHandler.bind(this);
        if (window.addEventListener) {
            window.addEventListener('scroll', handler, false);
        } else if (window.attachEvent) {
            window.attachEvent('onscroll', handler);
        }
    }

    var _timer = null;

    function _scrollHandler(ev) {
        clearTimeout(_timer);
        var self = this;
        _timer = setTimeout(function () {
            var topIndent = document.documentElement.scrollTop || document.body.scrollTop,
                w = window,
                d = document,
                e = d.documentElement,
                g = d.body,
                // x = w.innerWidth || e.clientWidth || g.clientWidth,
                windowHeight = w.innerHeight || e.clientHeight || g.clientHeight,
                bottomIndent = topIndent + windowHeight;

            self.listeners.forEach(function (cb) {
                cb(topIndent, bottomIndent);
            });
        }, this.timeout);
    }

    OnScroll.prototype.onScroll = function (cb) {
        this.listeners.push(cb);
    };

    OnScroll.prototype.offScroll = function (cb) {
        this.listeners = this.listeners.filter(function (listener) {
            return cb !== listener;
        })
    };

    return OnScroll;
})();