How to import SignalR in React Component?

Question

I have used create-react-app to scaffold the initial react application.

My DashBoard component:

import React, { Component } from 'react';
import { Link } from 'react-router-dom';
import $ from 'jquery';
import 'signalr';

class Dashboard extends Component {
   constructor(props) {    
   super(props);
   var connection = $.hubConnection('http://[address]:[port]');
   var proxy = connection.createHubProxy('[hubname]');   

    // atempt connection, and handle errors
    connection.start()
    .done(function(){ console.log('Now connected, connection ID=' + connection.id); })
    .fail(function(){ console.log('Could not connect'); });
}

  render() {
    return (...);
  }
}

export default Dashboard;

Now I get the below error from SignalR saying jQuery is not added, but I have imported it in the line above:

Error: jQuery was not found. Please ensure jQuery is referenced before the SignalR client JavaScript file.

If I comment out import "signalr"; jQuery gets loaded correctly and i can access the $ inside the module. Why does this happen?

Answer 1

This is how we do it now (year 2020) with the new package @microsoft/signalr. We use Redux, but you don't have to use Redux to be able to utilize this method.

If you are using @microsoft/signalr package instead of @aspnet/signalr, then this is how you can set it up. This is our working code in prod:

import {
  JsonHubProtocol,
  HubConnectionState,
  HubConnectionBuilder,
  LogLevel
} from '@microsoft/signalr';

const isDev = process.env.NODE_ENV === 'development';

const startSignalRConnection = async connection => {
  try {
    await connection.start();
    console.assert(connection.state === HubConnectionState.Connected);
    console.log('SignalR connection established');
  } catch (err) {
    console.assert(connection.state === HubConnectionState.Disconnected);
    console.error('SignalR Connection Error: ', err);
    setTimeout(() => startSignalRConnection(connection), 5000);
  }
};

// Set up a SignalR connection to the specified hub URL, and actionEventMap.
// actionEventMap should be an object mapping event names, to eventHandlers that will
// be dispatched with the message body.
export const setupSignalRConnection = (connectionHub, actionEventMap = {}, getAccessToken) => (dispatch, getState) => {
  const options = {
    logMessageContent: isDev,
    logger: isDev ? LogLevel.Warning : LogLevel.Error,
    accessTokenFactory: () => getAccessToken(getState())
  };
  // create the connection instance
  // withAutomaticReconnect will automatically try to reconnect
  // and generate a new socket connection if needed
  const connection = new HubConnectionBuilder()
    .withUrl(connectionHub, options)
    .withAutomaticReconnect()
    .withHubProtocol(new JsonHubProtocol())
    .configureLogging(LogLevel.Information)
    .build();

  // Note: to keep the connection open the serverTimeout should be
  // larger than the KeepAlive value that is set on the server
  // keepAliveIntervalInMilliseconds default is 15000 and we are using default
  // serverTimeoutInMilliseconds default is 30000 and we are using 60000 set below
  connection.serverTimeoutInMilliseconds = 60000;

  // re-establish the connection if connection dropped
  connection.onclose(error => {
    console.assert(connection.state === HubConnectionState.Disconnected);
    console.log('Connection closed due to error. Try refreshing this page to restart the connection', error);
  });

  connection.onreconnecting(error => {
    console.assert(connection.state === HubConnectionState.Reconnecting);
    console.log('Connection lost due to error. Reconnecting.', error);
  });

  connection.onreconnected(connectionId => {
    console.assert(connection.state === HubConnectionState.Connected);
    console.log('Connection reestablished. Connected with connectionId', connectionId);
  });

  startSignalRConnection(connection);

  connection.on('OnEvent', res => {
    const eventHandler = actionEventMap[res.eventType];
    eventHandler && dispatch(eventHandler(res));
  });

  return connection;
};

Then you would call like the following. Please note that this a pseudo code. You may have to call it differently depending on your project setup.

import { setupSignalRConnection } from 'fileAbove.js';

const connectionHub = '/hub/service/url/events';

export const setupEventsHub = setupSignalRConnection(connectionHub, {
  onMessageEvent: someMethod
}, getAccessToken);

export default () => dispatch => {
  dispatch(setupEventsHub); // dispatch is coming from Redux
};

Let me know if it helped by up-voting. Thank you