Function getOffsets

code/communication/public/app.js:6369–6399

* @param {DOMElement} outerNode * @return {?object}

(outerNode)

 * @return {?object}
 */
function getOffsets(outerNode) {
  var selection = window.getSelection && window.getSelection();

  if (!selection || selection.rangeCount === 0) {
    return null;
  }

  var anchorNode = selection.anchorNode,
      anchorOffset = selection.anchorOffset,
      focusNode = selection.focusNode,
      focusOffset = selection.focusOffset;

  // In Firefox, anchorNode and focusNode can be "anonymous divs", e.g. the
  // up/down buttons on an <input type="number">. Anonymous divs do not seem to
  // expose properties, triggering a "Permission denied error" if any of its
  // properties are accessed. The only seemingly possible way to avoid erroring
  // is to access a property that typically works for non-anonymous divs and
  // catch any error that may otherwise arise. See
  // https://bugzilla.mozilla.org/show_bug.cgi?id=208427

  try {
    /* eslint-disable no-unused-expressions */
    anchorNode.nodeType;
    focusNode.nodeType;
    /* eslint-enable no-unused-expressions */
  } catch (e) {
    return null;
  }

  return getModernOffsetsFromPoints(outerNode, anchorNode, anchorOffset, focusNode, focusOffset);
}

/**
 * Returns {start, end} where `start` is the character/codepoint index of