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ExpressEmitter

ExpressEmitter is the event-pattern primitive underneath Ingest routing. ActionRouter extends it directly, which is why route patterns, wildcards, and named params behave the way they do.

This class lives in @stackpress/lib, not in Ingest itself, but it explains a large part of how route matching works.

import ExpressEmitter from '@stackpress/lib/ExpressEmitter';

const emitter = new ExpressEmitter('/');

Why it matters in Ingest

Ingest routes are event matches.

ActionRouter turns routes like GET /users/:id into event patterns and then lets ExpressEmitter do the matching and extraction work.

router.get('/users/:id', ({ req, res }) => {
  res.setJSON({ id: req.data('id') });
});

router.get('/files/*', ({ req, res }) => {
  res.setJSON({ args: req.data() });
});

router.get('/assets/**', ({ req, res }) => {
  res.setJSON({ args: req.data() });
});

Pattern types

The important pattern shapes are:

  • :name for named params
  • * for one path segment
  • ** for the rest of a path

Those patterns are converted into regular expressions and stored as event expressions.

What it extracts

When an event matches:

  • named params become data.params
  • wildcard matches become data.args

In Ingest, ActionRouter then merges those into req.data(), which is why route handlers usually read params directly from the main request data object instead of from a separate matcher object.

Matching example

router.get('/users/:id', ({ req, res }) => {
  res.setJSON({
    id: req.data('id')
  });
});

router.get('/files/*', ({ req, res }) => {
  res.setJSON({
    pathPart: req.data('0')
  });
});

That behavior comes from the underlying event match, not from a separate route-param subsystem.

Expressions and listeners

ExpressEmitter also explains two maps that show up in the router API:

  • expressions
  • listeners
console.log(router.expressions);
console.log(router.listeners);

expressions holds the compiled route patterns. listeners holds the task queues attached to those events. Together, those structures are what make route introspection and tooling possible.

Relation to ActionRouter

ActionRouter adds three important pieces on top of ExpressEmitter:

  • HTTP method route helpers like get() and post()
  • request/response props creation
  • merging matched params and args into req.data()

So if you want to understand route syntax, pattern matching, or event priority behavior, ExpressEmitter is the right primitive to keep in mind. If you want the framework-level handler model, go back up to ActionRouter and Router.

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