jjmu15

// Determine if an element is in the visible viewport
function isInViewport(element) {
  var rect = element.getBoundingClientRect();
  var html = document.documentElement;
  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (window.innerHeight || html.clientHeight) &&
    rect.right <= (window.innerWidth || html.clientWidth)
  );

cvrebert

Test apparatus: http://jsfiddle.net/hRub4/

(Windows = Windows 8.1 desktop)

• Windows Chrome 39
  • Button focuses on click and via keyboard tabbing
  • Anchor focuses on click and via keyboard tabbing
• Windows Firefox 30.0
  • Button focuses on click and via keyboard tabbing
  • Anchor focuses on click and via keyboard tabbing
• Windows Internet Explorer 11