Events

Create and route custom events in Node.js

Custom Events

Events are plain JavaScript objects with a type field:

const event = { type: "AnalyzeEvent", text: "hello", score: 0.9 };

No classes needed — any object with type is an event.

Built-in Events

• "blazen::StartEvent" — the input event, carries your workflow input as properties
• "blazen::StopEvent" — terminates the workflow, must have a result field

// Start event (created by wf.run()):
{ type: "blazen::StartEvent", message: "hello" }

// Stop event (returned by a step):
{ type: "blazen::StopEvent", result: { answer: 42 } }

Event Routing

Steps declare which event types they handle in the addStep call:

wf.addStep("first", ["blazen::StartEvent"], async (event, ctx) => {
  return { type: "AnalyzeEvent", text: event.message };
});

wf.addStep("second", ["AnalyzeEvent"], async (event, ctx) => {
  return { type: "blazen::StopEvent", result: { text: event.text } };
});

Fan-out (Multiple Events)

Return an array to dispatch multiple events:

wf.addStep("fan", ["blazen::StartEvent"], async (event, ctx) => {
  return [
    { type: "BranchA", value: "a" },
    { type: "BranchB", value: "b" },
  ];
});

Side-Effect Steps

Return null and use ctx.sendEvent() for manual routing:

wf.addStep("side_effect", ["blazen::StartEvent"], async (event, ctx) => {
  await ctx.set("processed", true);
  await ctx.sendEvent({ type: "Continue" });
  return null;
});