Destinations

Destinations are where Junction sends your events. Each destination is a plain object with three async functions — init, transform, and send — wired together by the collector at runtime.

Available Destinations

Destination	Package	Runtime
Google Analytics 4	@junctionjs/destination-ga4	Client + Server
Amplitude	@junctionjs/destination-amplitude	Client + Server
Meta Pixel + CAPI	@junctionjs/destination-meta	Client + Server
Plausible	@junctionjs/destination-plausible	Client
HTTP (Generic)	@junctionjs/destination-http	Server

Configuration Pattern

Every destination is registered on the collector via its config:

import { createCollector } from "@junctionjs/core";
import { ga4 } from "@junctionjs/destination-ga4";

const collector = createCollector({
  destinations: [
    {
      destination: ga4,
      config: {
        measurementId: "G-XXXXXXXXXX",
      },
    },
  ],
});

Destinations are factory functions or pre-built objects — never classes. This keeps them tree-shakeable and easy to test.

Event Name Mapping

All destinations use a 3-tier fallback to resolve event names:

1. Config override — config.eventNameMap["product:viewed"] takes priority
2. Default map — each destination ships with sensible defaults for common events
3. Generated name — if no mapping exists, the name is derived from entity_action (or a destination-specific format)

// Example: override a single event name for GA4
{
  destination: ga4,
  config: {
    measurementId: "G-XXXXXXXXXX",
    eventNameMap: {
      "product:viewed": "my_custom_view_item",
    },
  },
}

Default Event Mapping

Junction Event	GA4	Amplitude	Meta
page:viewed	page_view	Page Viewed	PageView
product:viewed	view_item	Product Viewed	ViewContent
product:added	add_to_cart	Product Added	AddToCart
order:completed	purchase	Order Completed	Purchase

System Events

The _system entity is reserved for Junction’s internal lifecycle events (e.g., _system:initialized). All destinations must return null from transform() for system events — they are never forwarded to external providers.

Writing a Custom Destination

Junction destinations implement the Destination interface:

interface Destination<TConfig> {
  name: string;
  version: string;
  consent: ConsentCategory[];
  runtime: "client" | "server" | "both";

  init: (config: TConfig) => Promise<void> | void;
  transform: (event: JctEvent, config: TConfig) => unknown | null;
  send: (payload: unknown, config: TConfig) => Promise<void>;
  onConsent?: (state: ConsentState) => void;
  teardown?: () => Promise<void> | void;
}

See the Contributing Guide for the full walkthrough on building a new destination.