src/index.js
function getKey (node) {
  if (node.nodeType !== ELEMENT_TYPE) return
  var key = node.getAttribute(setDOM.KEY) || node.id
  if (key) return KEY_PREFIX + key
}
function getKey (node) {
  if (node.nodeType !== ELEMENT_TYPE) return
  var key = node.getAttribute(setDOM.KEY) || node.id
  if (key) return KEY_PREFIX + key
}
@private
@description
Utility to try to pull a key out of an element.
Uses 'data-key' if possible and falls back to 'id'.

@param {Node} node - The node to get the key for.
@return {string|void}