Listening To Activities

An Activity is the Teams‑specific payload that flows between the user and your bot.
Where events describe high‑level happenings inside your app, activities are the raw Teams messages such as chat text, card actions, installs, or invoke calls.
The Teams AI Library v2 exposes a fluent router so you can subscribe to these activities with app.on('<route>', …).

Here is an example of a basic message handler:

app.on('message', async ({ activity, send }) => {
  await send(`You said: ${activity.text}`);
});

In the above example, the activity parameter is of type MessageActivity, which has a text property. You'll notice that the handler here does not return anything, but instead handles it by sending a message back. For message activities, Teams does not expect your application to return anything (though it's usually a good idea to send some sort of friendly acknowledgment!).

Other activity types have different properties and different required results. For a given handler, the library will automatically determine the type of activity and also enforce the correct return type.

Middleware pattern

The on activity handlers follow a middleware pattern similar to how express middlewares work. This means that for each activity handler, a next function is passed in which can be called to pass control to the next handler. This allows you to build a chain of handlers that can process the same activity in different ways.

app.on('message', async ({ next }) => {
  console.log('global logger');
  next(); // pass control onward
});

app.on('message', async ({ activity, next }) => {
  if (activity.text === '/help') {
    await send('Here are all the ways I can help you...');
    return;
  }

  // Conditionally pass control to the next handler
  next();
});

app.on('message', async ({ activity }) => {
  // Fallthrough to the final handler
  await send(`Hello! you said ${activity.text}`);
});

info

Just like other middlewares, if you stop the chain by not calling next(), the activity will not be passed to the next handler.

Activity Reference

For a list of supported activities that your application can listen to, see the activity reference.