Check if an element is in the viewport

isOnScreen

( function ( $ ) {

    $.fn.isOnScreen = function () {

        var win = $( window ),
            bounds = this.offset(),
            viewport = {
                top: win.scrollTop(),
                left: win.scrollLeft()
            };

        viewport.right = viewport.left + win.width();
        viewport.bottom = viewport.top + win.height();

        bounds.right = bounds.left + this.outerWidth();
        bounds.bottom = bounds.top + this.outerHeight();

        return ( !( viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top ||
            viewport.top > bounds.bottom ) );
    };

} )( jQuery );