Add af and referrer to default referral query parameters

[yosriady]

Summary

Expanded the default referral code query parameters to include af (affiliate) and referrer parameters, in addition to the existing ref, referral, and refcode parameters. This allows the SDK to capture more common referral attribution sources out of the box.

Key Changes

• Added af and referrer to default referral parameters: Extended DEFAULT_REFERRAL_PARAMS constant to include these additional attribution parameters in the order: ref, referral, refcode, af, referrer
• Centralized parameter definitions: Created DEFAULT_REFERRAL_PARAMS constant in src/event/constants.ts to serve as the single source of truth for default referral parameters
• Updated page properties exclusion: Modified PAGE_PROPERTIES_EXCLUDED_FIELDS to use the new DEFAULT_REFERRAL_PARAMS constant instead of hardcoding individual parameter names
• Updated EventFactory: Replaced hardcoded default parameter list with reference to DEFAULT_REFERRAL_PARAMS constant
• Updated ReferralOptions documentation: Updated JSDoc to reflect the new default parameters and provided a more realistic example
• Added comprehensive test coverage: Added new test suite "Referral code parameter (default query params)" with tests for:
  • Each individual parameter being captured into context.ref
  • Proper separation of ?referrer query parameter from document.referrer
  • Parameter precedence (first parameter in the list wins)
  • Updated existing test to verify af parameter is excluded from page properties

Implementation Details

• Parameters are checked in order, with the first present parameter supplying the referral code
• The referrer parameter is intentionally included to capture referral codes, while being kept separate from the document.referrer property (which represents the external entry URL)
• All referral parameters are excluded from page event properties to prevent them from polluting analytics data
• The constant is kept in sync with the ReferralOptions.queryParams JSDoc default value

https://claude.ai/code/session_01NE7oDonRuxxDrNLe9Kfme3

---

^{Need help on this PR? Tag /codesmith with what you need. Autofix is disabled.}

[gemini-code-assist]

Code Review

This pull request extracts the default referral parameters into a shared constant DEFAULT_REFERRAL_PARAMS and expands the default list to include af and referrer. It also updates the excluded page properties, documentation, and adds comprehensive unit tests for the new default parameters. The feedback suggests simplifying the ternary expression in EventFactory.ts using optional chaining to improve readability.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[gemini-code-assist]

This ternary expression can be simplified and made more readable by using optional chaining (?.) directly. This avoids the negated ternary check and redundant references to DEFAULT_REFERRAL_PARAMS.

    const referralParams = this.options?.referral?.queryParams ?? DEFAULT_REFERRAL_PARAMS;