Quickstart: Create a serverless app with Azure Functions and SignalR Service using JavaScript

In this article, you use Azure SignalR Service, Azure Functions, and JavaScript to build a serverless application to broadcast messages to clients.


This quickstart can be run on macOS, Windows, or Linux.

Prerequisite Description
An Azure subscription If you don't have a subscription, create an Azure free account
A code editor You need a code editor such as Visual Studio Code.
Azure Functions Core Tools Requires version 4.0.5611 or higher to run Node.js v4 programming model.
Node.js LTS See supported node.js versions in the Azure Functions JavaScript developer guide.
Azurite SignalR binding needs Azure Storage. You can use a local storage emulator when a function is running locally.
Azure CLI Optionally, you can use the Azure CLI to create an Azure SignalR Service instance.

Create an Azure SignalR Service instance

In this section, you create a basic Azure SignalR instance to use for your app. The following steps use the Azure portal to create a new instance, but you can also use the Azure CLI. For more information, see the az signalr create command in the Azure SignalR Service CLI Reference.

  1. Sign in to the Azure portal.
  2. In the upper-left side of the page, select + Create a resource.
  3. On the Create a resource page, in the Search services and marketplace text box, enter signalr and then select SignalR Service from the list.
  4. On the SignalR Service page, select Create.
  5. On the Basics tab, you enter the essential information for your new SignalR Service instance. Enter the following values:
Field Suggested Value Description
Subscription Choose your subscription Select the subscription you want to use to create a new SignalR Service instance.
Resource group Create a resource group named SignalRTestResources Select or create a resource group for your SignalR resource. It's useful to create a new resource group for this tutorial instead of using an existing resource group. To free resources after completing the tutorial, delete the resource group.

Deleting a resource group also deletes all of the resources that belong to the group. This action can't be undone. Before you delete a resource group, make certain that it doesn't contain resources you want to keep.

For more information, see Using resource groups to manage your Azure resources.
Resource name testsignalr Enter a unique resource name to use for the SignalR resource. If testsignalr is already taken in your region, add a digit or character until the name is unique.

The name must be a string of 1 to 63 characters and contain only numbers, letters, and the hyphen (-) character. The name can't start or end with the hyphen character, and consecutive hyphen characters aren't valid.
Region Choose your region Select the appropriate region for your new SignalR Service instance.

Azure SignalR Service isn't currently available in all regions. For more information, see Azure SignalR Service region availability
Pricing tier Select Change and then choose Free (Dev/Test Only). Choose Select to confirm your choice of pricing tier. Azure SignalR Service has three pricing tiers: Free, Standard, and Premium. Tutorials use the Free tier, unless noted otherwise in the prerequisites.

For more information about the functionality differences between tiers and pricing, see Azure SignalR Service pricing
Service mode Choose the appropriate service mode Use Default when you host the SignalR hub logic in your web apps and use SignalR service as a proxy. Use Serverless when you use Serverless technologies such as Azure Functions to host the SignalR hub logic.

Classic mode is only for backward compatibility and isn't recommended to use.

For more information, see Service mode in Azure SignalR Service.

You don't need to change the settings on the Networking and Tags tabs for the SignalR tutorials.

  1. Select the Review + create button at the bottom of the Basics tab.
  2. On the Review + create tab, review the values and then select Create. It takes a few moments for deployment to complete.
  3. When the deployment is complete, select the Go to resource button.
  4. On the SignalR resource page, select Keys from the menu on the left, under Settings.
  5. Copy the Connection string for the primary key. You need this connection string to configure your app later in this tutorial.

Setup function project

Make sure you have Azure Functions Core Tools installed.

  1. Open a command line.
  2. Create project directory and then change into it.
  3. Run the Azure Functions func init command to initialize a new project.
func init --worker-runtime javascript --language javascript --model V4

Create the project functions

After you initialize a project, you need to create functions. This project requires three functions:

  • index: Hosts a web page for a client.
  • negotiate: Allows a client to get an access token.
  • broadcast: Uses a time trigger to periodically broadcast messages to all clients.

When you run the func new command from the root directory of the project, the Azure Functions Core Tools creates the function source files storing them in a folder with the function name. You edit the files as necessary replacing the default code with the app code.

Create the index function

  1. Run the following command to create the index function.

    func new -n index -t HttpTrigger
  2. Edit src/functions/httpTrigger.js and replace the contents with the following json code:

    const { app } = require('@azure/functions');
    const fs = require('fs').promises;
    const path = require('path');
    app.http('index', {
        methods: ['GET', 'POST'],
        authLevel: 'anonymous',
        handler: async (request, context) => {
            try {
                context.log(`Http function processed request for url "${request.url}"`);
                const filePath = path.join(__dirname,'../content/index.html');
                const html = await fs.readFile(filePath);
                return {
                    body: html,
                    headers: {
                        'Content-Type': 'text/html'
            } catch (error) {
                return {
                    status: 500,
                    jsonBody: error

Create the negotiate function

  1. Run the following command to create the negotiate function.

    func new -n negotiate -t HttpTrigger
  2. Edit src/functions/negotiate.js and replace the contents with the following json code:

    const { app, input } = require('@azure/functions');
    const inputSignalR = input.generic({
        type: 'signalRConnectionInfo',
        name: 'connectionInfo',
        hubName: 'serverless',
        connectionStringSetting: 'SIGNALR_CONNECTION_STRING',
    app.post('negotiate', {
        authLevel: 'anonymous',
        handler: (request, context) => {
            try {
                return { body: JSON.stringify(context.extraInputs.get(inputSignalR)) }
            } catch (error) {
                return {
                    status: 500,
                    jsonBody: error
        route: 'negotiate',
        extraInputs: [inputSignalR],

Create a broadcast function.

  1. Run the following command to create the broadcast function.

    func new -n broadcast -t TimerTrigger
  2. Edit src/functions/broadcast.js and replace the contents with the following code:

    const { app, output } = require('@azure/functions');
    const getStars = require('../getStars');
    var etag = '';
    var star = 0;
    const goingOutToSignalR = output.generic({
        type: 'signalR',
        name: 'signalR',
        hubName: 'serverless',
        connectionStringSetting: 'SIGNALR_CONNECTION_STRING',
    app.timer('sendMessasge', {
        schedule: '0 * * * * *',
        extraOutputs: [goingOutToSignalR],
        handler: async (myTimer, context) => {
            try {
                const response = await getStars(etag);
                if(response.etag === etag){
                    console.log(`Same etag: ${response.etag}, no need to broadcast message`);
                etag = response.etag;
                const message = `${response.stars}`;
                        'target': 'newMessage',
                        'arguments': [message]
            } catch (error) {

Create the index.html file

The client interface for this app is a web page. The index function reads HTML content from the content/index.html file.

  1. Create a folder called content in your project root folder.

  2. Create the file content/index.html.

  3. Copy the following content to the content/index.html file and save it:

      <h1>Azure SignalR Serverless Sample</h1>
      <div>Instructions: Goto <a href="https://github.com/Azure/azure-signalr">GitHub repo</a> and star the repository.</div>
      <div>Star count: <div id="messages"></div></div>
      <script src="https://cdnjs.cloudflare.com/ajax/libs/microsoft-signalr/8.0.0/signalr.min.js"></script>
        let messages = document.querySelector('#messages');
        const apiBaseUrl = window.location.origin;
        console.log(`apiBaseUrl: ${apiBaseUrl}`);
        const connection = new signalR.HubConnectionBuilder()
            .withUrl(apiBaseUrl + '/api')
          connection.on('newMessage', (message) => {
            console.log(`message: ${message}`);
            document.getElementById("messages").innerHTML = message;

Setup Azure Storage

Azure Functions requires a storage account to work. Choose either of the two following options:

  • Run the free Azure Storage Emulator.
  • Use the Azure Storage service. This may incur costs if you continue to use it.
  1. Start the Azurite storage emulator:

    azurite -l azurite -d azurite\debug.log
  2. Make sure the AzureWebJobsStorage in local.settings.json set to UseDevelopmentStorage=true.

Add the SignalR Service connection string to the function app settings

You're almost done now. The last step is to set the SignalR Service connection string in Azure Function app settings.

  1. In the Azure portal, go to the SignalR instance you deployed earlier.

  2. Select Keys to view the connection strings for the SignalR Service instance.

    Screenshot of Azure SignalR service Keys page.

  3. Copy the primary connection string, and execute the command:

    func settings add AzureSignalRConnectionString "<signalr-connection-string>"

Run the Azure Function app locally

Run the Azure Function app in the local environment:

func start

After the Azure Function is running locally, go to http://localhost:7071/api/index. The page displays the current star count for the GitHub Azure/azure-signalr repository. When you star or unstar the repository in GitHub, you'll see the refreshed count every few seconds.

Having issues? Try the troubleshooting guide or let us know.

Clean up resources

If you're not going to continue to use this app, delete all resources created by this quickstart with the following steps so you don't incur any charges:

  1. In the Azure portal, select Resource groups on the far left, and then select the resource group you created. Alternatively, you may use the search box to find the resource group by its name.

  2. In the window that opens, select the resource group, and then click Delete resource group.

  3. In the new window, type the name of the resource group to delete, and then click Delete.

Sample code

You can get all code used in the article from GitHub repository:

Next steps

In this quickstart, you built and ran a real-time serverless application in localhost. Next, learn more about how to bi-directional communicating between clients and Azure Function with SignalR Service.