jQuery Inview

gistfile1.js

$.extend($.expr[':'], {
    inview: function(el) {
        var e = $(el),
            w = $(window),
            wt = w.scrollTop(),
            wb = wt + w.height(),
            et = e.offset().top,
            eb = et + e.height();

        return eb >= wt && et <= wb;
    }
});