JavaScript Navigator vendorSub Property

What You’ll Learn

navigator.vendorSub is a Baseline Navigator property. Per MDN, its value is always the empty string in any browser. Learn what that means, how it differs from vendor, five examples, and why sniffing with it is useless.

Introduction

Next to navigator.vendor sits navigator.vendorSub — a companion “sub” field that sounds like it should hold a vendor version or subtitle.

In reality, MDN is crystal clear: the value is always the empty string, in any browser.

Learn it so legacy Navigator tables make sense — then ignore it for real app logic.

Understanding the vendorSub Property

Think of vendorSub as a reserved legacy slot that modern browsers keep empty for compatibility — similar in spirit to other fixed Navigator labels.

• Always "" in conforming / mainstream browsers (MDN).
• Read-only — you inspect, you do not assign.
• Cannot identify Chrome, Firefox, Safari, or Edge.
• Pair it with vendor only for learning: vendor may vary; vendorSub does not.
• Related date-like sibling: productSub (not empty — returns fixed tokens).

📝 Syntax

General form of the property:

navigator.vendorSub

Value

• The empty string ("").

Common patterns

console.log(navigator.vendorSub); // ""

// Always true in modern browsers:
const isEmpty = navigator.vendorSub === "";

console.log(typeof navigator.vendorSub); // "string"
console.log(navigator.vendorSub.length); // 0

// Prefer feature detection for real features:
if ("serviceWorker" in navigator) {
  // safe to use service workers
}

Examples Gallery

Examples follow MDN navigator.vendorSub behavior. Prefer Try It Yourself — you should see an empty string in any modern browser.

console.log(JSON.stringify(navigator.vendorSub));

""

const isEmpty = navigator.vendorSub === "";
console.log("vendorSub === \"\": " + isEmpty);
console.log("This does NOT identify a browser brand.");

vendorSub === "": true
This does NOT identify a browser brand.

const v = navigator.vendorSub;
const lines = [
  "value: " + JSON.stringify(v),
  "typeof: " + typeof v,
  "length: " + v.length,
  "is undefined?: " + (v === undefined),
  "is null?: " + (v === null)
];
console.log(lines.join("\n"));

value: ""
typeof: string
length: 0
is undefined?: false
is null?: false

const lines = [
  "vendor: " + JSON.stringify(navigator.vendor),
  "vendorSub: " + JSON.stringify(navigator.vendorSub),
  "productSub: " + JSON.stringify(navigator.productSub)
];
console.log(lines.join("\n"));
console.log("vendorSub stays empty even when vendor is not.");

vendor: "Google Inc."
vendorSub: ""
productSub: "20030107"
vendorSub stays empty even when vendor is not.
(vendor / productSub vary by browser)

const lines = [];
lines.push(
  "vendorSub: " + JSON.stringify(navigator.vendorSub) + " — always empty"
);
lines.push(
  "serviceWorker: " +
    ("serviceWorker" in navigator ? "available" : "missing") +
    " — use this for features"
);
console.log(lines.join("\n"));

vendorSub: "" — always empty
serviceWorker: available — use this for features

🚀 Common Use Cases

• Learning Navigator history — know why the property exists but stays blank.
• Legacy code review — spot useless checks on vendorSub.
• Interview / trivia — “What does vendorSub return?” → always "".
• Not for browser detection — empty everywhere.
• Not for versioning — there is no vendor subtitle to parse.

📝 Notes

• Baseline Widely available (MDN, since July 2015).
• Not Deprecated, Experimental, or Non-standard — no status banner required.
• Always the empty string "" in any browser (MDN).
• Read-only string on Navigator.
• Related: virtualKeyboard, vendor, productSub, product.

💡 Best Practices