JavaScript Navigator productSub Property

What You’ll Learn

navigator.productSub is a legacy Navigator property. Per MDN it returns either "20030107" or "20100101". Learn the typical values, why sniffing is a bad idea, five examples, and better alternatives.

Introduction

The name productSub looks like a build or product version date. In practice it is a fixed compatibility string that browsers expose as either "20030107" or "20100101".

MDN notes the usual pattern: Apple Safari and Google Chrome return "20030107"; Firefox returns "20100101". Older Internet Explorer returned undefined.

It sits next to navigator.product in the same family of old identification labels.

Understanding the productSub Property

productSub is a read-only string on Navigator (or undefined in legacy IE). The date-like shape is historical; modern engines keep a constant token for compatibility.

• Value is either "20030107" or "20100101" in modern browsers.
• Chrome, Chromium Edge, Safari: typically "20030107".
• Firefox: typically "20100101".
• IE: historically undefined.
• Not a reliable way to identify brands in new code.

📝 Syntax

General form of the property:

navigator.productSub

Value

• Either "20030107" or "20100101".
• May be undefined in very old Internet Explorer.

Common patterns

console.log(navigator.productSub);
// Chrome / Safari: "20030107"
// Firefox: "20100101"

const known = ["20030107", "20100101"];
const isKnownToken = known.includes(navigator.productSub);

// Prefer feature detection instead of sniffing:
if ("serviceWorker" in navigator) {
  // safe to use service workers
}

Examples Gallery

Examples follow MDN navigator.productSub behavior. Prefer Try It Yourself — Chromium/Safari often show 20030107; Firefox shows 20100101.

console.log("productSub: " + navigator.productSub);

productSub: 20030107

const value = navigator.productSub;
let note = "other / missing";

if (value === "20030107") {
  note = "common Chromium / Safari token (MDN)";
} else if (value === "20100101") {
  note = "common Firefox token (MDN)";
}

console.log("value: " + value);
console.log("note: " + note);
console.log("Do not use this as a browser detector.");

value: 20030107
note: common Chromium / Safari token (MDN)
Do not use this as a browser detector.

const value = navigator.productSub;
const lines = [
  "value: " + String(value),
  "typeof: " + typeof value,
  "isDefined: " + (typeof value !== "undefined")
];
console.log(lines.join("\n"));

value: 20030107
typeof: string
isDefined: true

const lines = [
  "product: " + navigator.product,
  "productSub: " + navigator.productSub,
  "appCodeName: " + navigator.appCodeName,
  "appName: " + navigator.appName
];
console.log(lines.join("\n"));
console.log("These are compatibility labels — not brand detectors.");

product: Gecko
productSub: 20030107
appCodeName: Mozilla
appName: Netscape
These are compatibility labels — not brand detectors.

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

productSub: 20030107 — ignore for sniffing
serviceWorker: available — use this for features

🚀 Common Use Cases

• Learning Navigator history — understand the two fixed date-like tokens.
• Legacy code review — spot sniffing that branches on 20030107 / 20100101.
• Interview / trivia — know Chrome/Safari vs Firefox MDN notes.
• Not for browser detection — never gate features on productSub.
• Not for real versioning — it is not a trustworthy release date.

📝 Notes

• Baseline Widely available (MDN, since July 2015).
• Not Deprecated, Experimental, or Non-standard — no status banner required.
• Returns "20030107" or "20100101"; IE historically returned undefined.
• Read-only string on Navigator in modern browsers.
• Related: product, scheduling, appCodeName, Window.

💡 Best Practices