Convert Async Function to React Component

asyncToReact.js

function asyncToReact(fn) {
  class PromiseComponent extends React.Component {
    state = { waiting: true, result: null };
    componentDidMount() {
      fn(...this.props.args).then(result => this.setState({ waiting: false, result }));
    }
    componentDidUpdate() {
      fn(...this.props.args).then(result => this.setState({ waiting: false, result }));
    }
    shouldComponentUpdate(newProps) {
      return this.props.args.some((arg, i) => !shallowEquals(arg, newProps.args[i]));
    }
    render() {
      if (this.state.waiting) {
        return null; // TODO: When Fiber works, use async dependency placeholder.
      }
      return this.props.mapper(this.props.data);
    }
  };
  return function(...args) {
    return {
      then(mapper) {
        return <PromiseComponent mapper={mapper} args={args} />;
      }
    };
  }
}

fetch.js

fetch = asyncToReact(fetch);

• Do we need componentWillUnmount and "unsubscribe" for promise?
• What about reject?