Mailspring/internal_packages/open-tracking/lib/open-tracking-button.jsx

import {DraftStore, React, Actions, NylasAPI, DatabaseStore, Message, Rx} from 'nylas-exports'
import {RetinaImg} from 'nylas-component-kit'
import plugin from '../package.json'
const PLUGIN_ID = plugin.appId[NylasEnv.config.get("env")];

export default class OpenTrackingButton extends React.Component {

  static displayName = 'OpenTrackingButton';

  static propTypes = {
    draftClientId: React.PropTypes.string.isRequired,
  };

  constructor(props) {
    super(props);
    this.state = {enabled: false};
  }

  componentDidMount() {
    const query = DatabaseStore.findBy(Message, {clientId: this.props.draftClientId});
    this._subscription = Rx.Observable.fromQuery(query).subscribe(this.setStateFromDraft)
  }

  componentWillUnmount() {
    this._subscription.dispose();
  }

  setStateFromDraft = (draft)=> {
    if (!draft) return;
    const metadata = draft.metadataForPluginId(PLUGIN_ID);
    this.setState({enabled: metadata ? metadata.tracked : false});
  };

  _onClick=()=> {
    const currentlyEnabled = this.state.enabled;

    // write metadata into the draft to indicate tracked state
    DraftStore.sessionForClientId(this.props.draftClientId).then((session)=> {
      const draft = session.draft();

      NylasAPI.authPlugin(PLUGIN_ID, plugin.title, draft.accountId)
      .then(() => {
        Actions.setMetadata(draft, PLUGIN_ID, currentlyEnabled ? null : {tracked: true});
      })
      .catch((error)=> {
        NylasEnv.reportError(error);
        NylasEnv.showErrorDialog(`Sorry, we were unable to save your read receipt settings. ${error.message}`);
      });
    });
  };

  render() {
    const title = this.state.enabled ? "Disable" : "Enable";
    return (<button className={`btn btn-toolbar ${this.state.enabled ? "btn-enabled" : ""}`}
                   onClick={this._onClick} title={`${title} read receipts`}>
      <RetinaImg url="nylas://open-tracking/assets/icon-composer-eye@2x.png"
                 mode={RetinaImg.Mode.ContentIsMask} />
    </button>)
  }

}