Detecting when an iframe gets or loses focus

Question

What\'s the correct way of detecting when an iframe gets or loses focus (i.e. will or will not receive keyboard events)? The following is not working in Fx4:

Answer 1

A compact function that accepts callbacks you want to run when iframe gets or loses focus.

/* eslint-disable no-unused-vars */
export default function watchIframeFocus(onFocus, onBlur) {
  let iframeClickedLast;

  function windowBlurred(e) {
    const el = document.activeElement;
    if (el.tagName.toLowerCase() == 'iframe') {
      iframeClickedLast = true;
      onFocus();
    } 
  }
  function windowFocussed(e) {
    if (iframeClickedLast) {
      iframeClickedLast = false;
      onBlur();
    } 
  }
  window.addEventListener('focus', windowFocussed, true);  
  window.addEventListener('blur', windowBlurred, true);
}