Check if we have access to the iframe body.

isFriendlyIframe.js

/**
 * Determines if the passed iframe is a friendly iframe.
 *
 * @param {HTMLElement} iframe The iframe under test.
 * @return {boolean} True if friendly iframe, False otherwise.
 */
function isFriendlyIframe(iframe) {
  var html = null;
  try {
    // deal with older browsers
    var doc = iframe.contentDocument || iframe.contentWindow.document;
    html = doc.body.innerHTML;
  } catch (err) {
    // do nothing
  }
  return html !== null;
}