Validation

Why Validate?

Without validation, data quality issues are discovered weeks later when a funnel breaks, a report shows $0 revenue, or a destination silently drops malformed events. Junction catches these at the source.

Schema Contracts

Define contracts per entity+action pair using Zod:

import { z } from "zod";

const schemas = {
  "product:added": {
    version: "1.0.0",
    mode: "strict",
    schema: z.object({
      product_id: z.string().min(1),
      name: z.string().min(1),
      price: z.number().nonnegative(),
      currency: z.string().length(3),
      quantity: z.number().int().positive(),
    }),
  },
};

Validation Modes

Mode	Invalid Event Behavior
strict	Event is dropped, error logged
lenient	Warning logged, event passes through

Use strict for critical events (purchases, sign-ups) and lenient during development or for non-critical events.

What This Prevents

Scenario	Without Validation	With Junction
addToCart instead of product:added	Funnel breaks silently	Type error + runtime validation
Price sent as string "19.99"	Destination coerces unpredictably	Zod catches it
Missing product_id	GA4 event fires without item_id	Contract rejects, logged
New dev forgets currency field	Revenue reports show $0	Strict mode blocks the event

Adding Contracts to Your Config

import { createClient } from "@junctionjs/client";

const jct = createClient({
  schemas,
  destinations: [/* ... */],
});

Events without a matching contract pass through unvalidated. Add contracts incrementally — start with your most critical events.