code: function getComponentKey(component, index) {
    // Do some typechecking here since we call this blindly. We want to ensure
    // that we don't block potential future ES APIs.
    if (typeof component === 'object' && component !== null && component.key != null) {
      // Explicit key
      return escape(component.key);
    }
    // Implicit key determined by the index in the set
    return index.toString(36);
  }
docs: Generate a key string that identifies a component within a set.
  
  @param {*} component A component that could contain a manual key.
  @param {number} index Index that is used if a manual key is not provided.
  @return {string}