Check Visible - jQuery function to test presence of element on screen.

checkvisible.js

function checkvisible( elm ) {
  var vph = $(window).height(), // Viewport Height
    st = $(window).scrollTop(), // Scroll Top
    y = $(elm).offset().top;

  // test if element is on screen or has been scrolled past
  return (y < (vph + st));

  // test if element is on screen
  // return (y > st) && (y < (vph + st));
}