@thomasseanfahey/fp-lib

Offline DOM fingerprinting utilities.

This library computes deterministic structural fingerprints for DOM elements and injects them into the DOM as data-fp attributes. It contains compatibility exports matching the original fp-lib API, but runs entirely locally (no network, no keys, no subscriptions).

Install

npm i @thomasseanfahey/fp-lib

Core usage (browser)

import { init, querySelectors } from '@thomasseanfahey/fp-lib/browser';

// Inject fingerprints into the live DOM (legacy-compatible)
await init(document);

// Resolve elements using CSS selectors or fingerprint strings
const els = await querySelectors(document, {
  title: 'h1',
  buyButton: ['button.buy', 'button[data-testid="buy"]']
});

console.log(els.title?.getAttribute('data-fp'));

Lower-level primitives

import { computeFingerprints, injectFingerprints, findByFingerprint } from '@thomasseanfahey/fp-lib/browser';

const map = computeFingerprints(document.body);
injectFingerprints(document.body, map);

const fp = document.querySelector('h1')?.getAttribute('data-fp');
const h1 = fp ? findByFingerprint(document, fp) : null;

Notes

• No network calls. No telemetry. No API keys.
• Fingerprints are deterministic for a given DOM structure and the chosen heuristics.
• Structural drift (DOM reordering) will change fingerprints; for dynamic sites, consider selecting stable anchors and reinjecting after major re-renders. "# fp-lib"