Emit events

Like event sources, workflows can emit events. These events can trigger other workflows, or be consumed using Pipedream’s REST API.

Using `$.send.emit()` in workflows

You can emit arbitrary events from any Node.js code steps using $.send.emit().

export default defineComponent({
  async run({ steps, $ }) {
    $.send.emit({
      name: "Yoda",
    });
  }
});

$.send.emit() accepts an object with the following properties:

$.send.emit(
  event, // An object that contains the event you'd like to emit
  channel, // Optional, a string specifying the channel
);

Emitting events to channels

By default, events are emitted to the default channel. You can optionally emit events to a different channel, and listening sources or workflows can subscribe to events on this channel, running the source or workflow only on events emitted to that channel.

Pass the channel as the second argument to $.send.emit():

export default defineComponent({
  async run({ steps, $ }) {
    $.send.emit(
      {
        name: "Yoda",
      },
      'channel_name'
    );
  }
});

Using `$.send.emit()` in component actions

If you’re authoring a component action, you can emit data using $.send.emit().

$.send.emit() functions the same as $.send.emit() in workflow code steps:

export default defineComponent({
  async run({ steps, $ }) {
    $.send.emit({
      name: "Yoda",
    });
  }
})

Destination delivery is asynchronous: emits are sent after your workflow finishes.

You can call $.send.emit() multiple times within a workflow, for example: to iterate over an array of values and emit an event for each.

export default defineComponent({
  async run({ steps, $ }) {
    const names = ["Luke", "Han", "Leia", "Obi Wan"];
    for (const name of names) {
      $.send.emit({
        name,
      });
    }
  }
});

Trigger a workflow from emitted events

We call the events you emit from a workflow emitted events. Sometimes, you’ll want emitted events to trigger another workflow. This can be helpful when:

You process events from different workflows in the same way. For example, you want to log events from many workflows to Amazon S3 or a logging service. You can write one workflow that handles logging, then $.send.emit() events from other workflows that are consumed by the single, logging workflow. This helps remove duplicate logic from the other workflows.
Your workflow is complex and you want to separate it into multiple workflows to group logical functions together. You can $.send.emit() events from one workflow to another to chain the workflows together.

Here’s how to configure a workflow to listen for emitted events.

Currently, you can’t select emitted events as a workflow trigger from the Pipedream UI. We’ll show you how add the trigger via API. First, pick an existing workflow where you’d like to receive emitted events. If you want to start with a new workflow, just select the HTTP / Webhook trigger.
This workflow is called the listener. The workflow where you’ll use $.send.emit() is called the emitter. If you haven’t created the emitter workflow yet, do that now.
Get the workflow IDs of both the listener and emitter workflows. You’ll find the workflow ID in the workflow’s URL in your browser bar — it’s the p_abc123 in https://pipedream.com/@username/p_abc123/.
You can use the Pipedream REST API to configure the listener to receive events from the emitter. We call this creating a subscription. If your listener’s ID is p_abc123 and your emitter’s ID is p_def456, you can run the following command to create this subscription:

curl "https://api.pipedream.com/v1/subscriptions?emitter_id=dc_def456&listener_id=p_abc123" \
  -X POST \
  -H "Authorization: Bearer <api_key>" \
  -H "Content-Type: application/json"

Run your emitter workflow, emitting an event using $.send.emit():

export default defineComponent({
  async run({ steps, $ }) {
    $.send.emit({
      name: "Yoda",
    });
  }
});

This should trigger your listener, and you should see the same event in the event inspector.

Note: Please upvote this issue to see support for adding emitted events as a workflow trigger in the UI.

Consuming emitted events via REST API

$.send.emit() can emit any data you’d like. You can retrieve that data using Pipedream’s REST API endpoint for retrieving emitted events.

This can be helpful when you want a workflow to process data asynchronously using a workflow. You can save the results of your workflow with $.send.emit(), and only retrieve the results in batch when you need to using the REST API.

Emit logs / troubleshooting

Below your code step, you’ll see both the data that was sent in the emit. If you ran $.send.emit() multiple times within the same code step, you’ll see the data that was emitted for each.

HTTP SSE