Collected IDs

Collected IDs let you carry first-party identifiers that already live in the visitor’s browser — a loyalty ID in a cookie, a CRM segment in localStorage, a campaign ID in the URL — into your server-side pipeline, so any destination can use them. You name exactly what to collect; Datafly.js never reads anything you have not configured.

Once collected, a value is stored under the visitor’s identity and attached to later events automatically, so a one-time read keeps working on events that do not resend it.

What you configure

Each provider is one named value to collect, with:

• Name — the key the value is stored under and referenced by (e.g. loyalty_id).
• Type — where to read it from (see below).
• Type-specific setting — the cookie name, storage key, URL parameter, selector, or endpoint.
• Consent category (recommended) — the value is only collected when that consent category is granted.
• Collection timing — first visit only, or every page load.
• Cache — how long to reuse a collected value before reading again.

Source types

An optional parser can post-process the raw value — for example, extract the GA client ID from a _ga cookie, pull a field out of a JSON value, or match a regular expression.

Consent

Set a consent category on every provider that collects advertising- or marketing-related identifiers. When the visitor has not granted that category, Datafly.js skips the provider entirely — nothing is read and nothing is sent. Only collect what your consent notice and legal basis cover, and name each source explicitly; there is no “collect everything” option by design.

Using collected IDs in mappings

Collected values are available to any destination blueprint through the collected_ids.<name> source path:

global:
  mappings:
    - source: collected_ids.loyalty_id
      target: external_id
    - source: collected_ids.crm_segment
      target: user_properties.segment.value

This lets GA4, Meta, TikTok, a warehouse, or any other destination receive the identifier without each one reading the browser itself.

In the event payload

Collected values appear on the event under collected_ids:

{
  "type": "page",
  "collected_ids": {
    "loyalty_id": "LP-99831",
    "crm_segment": "vip"
  }
}

After the first event they are retained under the visitor’s identity and attached automatically, so the browser does not need to resend them every time.