JavaScript Navigator buildID Property

What You’ll Learn

navigator.buildID is a non-standard Navigator property that returns a build identifier string (historically YYYYMMDDHHMMSS). Learn feature detection, privacy fixed values in modern Firefox, why sniffing fails, five examples, and try-it labs.

Introduction

Some browsers historically exposed a build ID — a timestamp-like string that identified when that browser binary was built. That value lived on navigator.buildID.

MDN notes the property is non-standard (not part of a public standard) and that modern browsers may return a fixed timestamp as a privacy measure. In Firefox 64+, that example value is 20181001000000.

Understanding the buildID Property

When present, buildID is a read-only string. The documented shape is YYYYMMDDHHMMSS (year, month, day, hour, minute, second).

• Missing in many browsers (especially Chromium / Safari).
• Where present (commonly Firefox), the value may be a privacy constant.
• Useless for fingerprinting or precise version detection today.
• Always feature-detect with "buildID" in navigator.

📝 Syntax

General form of the property:

navigator.buildID

Value

• A string representing a build identifier (form YYYYMMDDHHMMSS), when supported.
• May be a fixed privacy placeholder in modern Firefox (for example 20181001000000).

Common patterns

if ("buildID" in navigator) {
  console.log(navigator.buildID);
} else {
  console.log("buildID not supported");
}

// Do not use for feature branching — prefer:
if ("serviceWorker" in navigator) {
  // …
}

Examples Gallery

Examples follow MDN Navigator.buildID behavior with safe detection. Use View Output or Try It Yourself for each case.

const supported = "buildID" in navigator;
console.log(supported ? "buildID available" : "buildID missing");

buildID missing
(or "available" in Firefox)

if (!("buildID" in navigator)) {
  console.log("buildID not supported");
} else {
  console.log(navigator.buildID);
}

buildID not supported
(or a string like 20181001000000 in Firefox)

function describeBuildId() {
  if (!("buildID" in navigator)) return "missing";
  const id = String(navigator.buildID);
  const ok = /^\d{14}$/.test(id);
  return "value=" + id + "; looksLikeYYYYMMDDHHMMSS=" + ok;
}

console.log(describeBuildId());

missing
(or value=20181001000000; looksLikeYYYYMMDDHHMMSS=true)

const FIXED_FX = "20181001000000";

if (!("buildID" in navigator)) {
  console.log("no buildID");
} else if (navigator.buildID === FIXED_FX) {
  console.log("matches Firefox privacy placeholder");
} else {
  console.log("other buildID: " + navigator.buildID);
}

no buildID
(or "matches Firefox privacy placeholder")

const lines = [];
lines.push(
  "buildID: " +
    ("buildID" in navigator ? navigator.buildID : "(absent)") +
    " — ignore for sniffing"
);
lines.push(
  "serviceWorker: " +
    ("serviceWorker" in navigator ? "available" : "missing")
);
console.log(lines.join("\n"));

buildID: (absent) — ignore for sniffing
serviceWorker: available
(exact lines depend on your browser)

🚀 Common Use Cases

• Learning Navigator — see a non-standard, browser-specific property.
• Legacy Firefox tooling — understand old build-stamp reads.
• Privacy education — show why unique build IDs were frozen.
• Not for production sniffing — prefer feature detection.
• Not for fingerprinting — modern values are often shared constants.

📝 Notes

• Non-standard — not part of a public web standard (MDN).
• Not labeled Deprecated or Experimental on MDN.
• Modern Firefox may return a fixed privacy timestamp.
• Do not use for version detection or fingerprinting.
• Related: appVersion, appName, Window.

💡 Best Practices