docs: function getID(node) {
    var id = internalGetID(node);
    if (id) {
      if (nodeCache.hasOwnProperty(id)) {
        var cached = nodeCache[id];
        if (cached !== node) {
          ("production" !== process.env.NODE_ENV ? invariant(
            !isValid(cached, id),
            'ReactMount: Two valid but unequal nodes with the same `%s`: %s',
            ATTR_NAME, id
          ) : invariant(!isValid(cached, id)));
  
          nodeCache[id] = node;
        }
      } else {
        nodeCache[id] = node;
      }
    }
  
    return id;
  }