JavaScript Navigator buildID Property

Beginner
5 min read
Updated: Nov 2026
3 examples
Property
Decorative image with the word BUILDID

Definition

navigator.buildID returns a string meant to be the browser’s build identifier (MDN), historically in the form YYYYMMDDHHMMSS.

Read the notes below before you rely on this property. Prefer feature detection when support is limited.

Syntax

Use navigator.buildID. Start with this line.

JavaScript
navigator.buildID
CallWhat it does
navigator.buildIDPrimary signature.

Built into the browser. Read navigator.buildID on Navigator — no import required.

Library declarations
JavaScript
navigator.buildID

Parameters

ParameterDescription
"buildID" in navigatorRequired. Feature detect

Return Value

Return ValueDescription
*The current value of navigator.buildID.

JavaScript Examples

Example 1 — Feature Detect

Check whether buildID exists before reading it.

JavaScript
if ("buildID" in navigator) {
  console.log("buildID supported");
  console.log(navigator.buildID);
} else {
  console.log("buildID missing");
}
Try It Yourself

How It Works

  1. Use in. Safe check before accessing the property.
  2. Branch. Many browsers omit buildID entirely.
  3. Read only if present. Avoid throwing or logging undefined by accident.
  4. No side effects. Detection alone does not change the browser.

Example 2 — Read the String

Log the value and its length when available.

JavaScript
const id = ("buildID" in navigator) ? navigator.buildID : null;

console.log("value:", id);
console.log("typeof:", id === null ? "n/a" : typeof id);
console.log("length:", id === null ? "n/a" : id.length);
Try It Yourself

How It Works

  1. Guard first. Store null when the property is absent.
  2. Read the string. Format is usually 14 digits when present.
  3. Inspect length. Helps confirm the YYYYMMDDHHMMSS shape.
  4. Do not parse for logic. Treat it as a curiosity, not a version API.

Example 3 — Privacy Placeholder Check

See if the value matches Firefox’s fixed privacy timestamp.

JavaScript
const FIXED = "20181001000000";

if (!("buildID" in navigator)) {
  console.log("buildID missing");
} else {
  const id = navigator.buildID;
  console.log("buildID:", id);
  console.log("looks like Firefox privacy placeholder:", id === FIXED);
  console.log("Do not use this for fingerprinting or version sniffing.");
}
Try It Yourself

How It Works

  1. Compare to the known constant. MDN cites 20181001000000 for modern Firefox.
  2. Interpret carefully. A match means a privacy placeholder — not a unique build.
  3. Skip sniffing. Same string for many users → useless for targeting builds.
  4. Prefer features. Branch on real APIs instead of build stamps.
Compatibility

Browser Support

navigator.buildID is marked Non-standard on MDN — not part of a public standard. Support is limited (historically Firefox-oriented).

✓ Non-standard · Limited

Navigator.buildID

Build identifier string (YYYYMMDDHHMMSS when present). Often missing; in modern Firefox may be a fixed privacy value.

Limited Non-standard
Google Chrome All versions · Desktop & Mobile
Full support
Mozilla Firefox All versions · Desktop & Mobile
Full support
Apple Safari All versions · macOS & iOS
Full support
Microsoft Edge All versions · Chromium & Legacy
Full support
Internet Explorer IE 6+ · Legacy environments
Full support
Opera All modern versions
Full support
buildID Check MDN

Bottom line: Fine for demos and legacy study. Never rely on it for product versioning, sniffing, or fingerprinting — use feature detection instead.

Frequently Asked Questions

A string meant to be the browser's build identifier, historically in the form YYYYMMDDHHMMSS. The property is non-standard and not available in every browser.
MDN marks it Non-standard (not part of a public standard). It is not labeled Deprecated or Experimental on MDN. Prefer not to rely on it in production.
For privacy, modern Firefox returns a fixed timestamp instead of a unique build ID that could help fingerprint users (from Firefox 64 onward, per MDN).
No — not reliably. It is missing in many browsers, and where present it may be a constant privacy placeholder rather than a real unique build stamp.
No. It is a read-only Navigator property when it exists.
Feature detection for APIs you need. Do not use buildID for version sniffing or fingerprinting.

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About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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