Browser Fingerprinting

With logged‑in users, identification is trivial. For anonymous users, we can use a browser fingerprint — a unique identifier derived from available device/browser attributes at a point in time. JS doesn’t expose “a fingerprint” directly; you have to compute it (libraries like FingerprintJS help).

FingerprintJS v3

Latest is v4, but v4 uses BSL (becomes MIT after 4 years). In 2024, v4 isn’t MIT yet, so v3 (MIT) is the safe open‑source choice.

Accuracy

• OSS accuracy ~40–60%; commercial ~99.5% (with server‑side components).
• Fingerprints often remain stable only for weeks.

Usage

const fpPromise = new FingerprintJS.load();
    fpPromise
      .then(fp => fp.get())
      .then(result => {
        const visitorId = result.visitorId;
        console.log(visitorId)
      })

References

• https://github.com/fingerprintjs/fingerprintjs/tree/v3