JavaScript Navigator appCodeName Property

What You’ll Learn

navigator.appCodeName is a legacy Navigator property. Per MDN, its value is always "Mozilla" in any browser — kept only for compatibility. Learn what it returns, why sniffing fails, five examples, and better alternatives.

Introduction

Long ago, sites checked the browser “code name” to decide which features to enable. That led to fragile sniffing. Today every major browser still reports appCodeName as "Mozilla" so old pages keep working.

So if you log navigator.appCodeName in Chrome, Edge, Firefox, or Safari, you will almost always see the same string: Mozilla.

Learn it so legacy code makes sense — then use feature detection for real apps.

Understanding the appCodeName Property

appCodeName is a read-only string on Navigator. Historically it meant “internal code name.” In practice it is a fixed compatibility value.

• Value is always "Mozilla" in conforming browsers.
• Kept for old scripts that expected that string.
• Useless for telling Chrome apart from Firefox or Safari.
• Part of the same legacy family as appName and related Navigator strings.

📝 Syntax

General form of the property:

navigator.appCodeName

Value

• The string "Mozilla".

Common patterns

console.log(navigator.appCodeName); // "Mozilla"

// Always true in modern browsers:
const isLegacyMozillaLabel =
  navigator.appCodeName === "Mozilla";

// Prefer feature detection instead of sniffing:
if ("geolocation" in navigator) {
  // safe to use navigator.geolocation
}

Examples Gallery

Examples follow MDN Navigator.appCodeName behavior. Use View Output or Try It Yourself for each case.

console.log(navigator.appCodeName);
// Mozilla

Mozilla

const codeName = navigator.appCodeName;
const isMozillaLabel = codeName === "Mozilla";

console.log(codeName);
console.log("isMozillaLabel: " + isMozillaLabel);
// Mozilla
// isMozillaLabel: true

Mozilla
isMozillaLabel: true

const name = navigator.appCodeName;
console.log(typeof name);
console.log(name.length);
console.log(name.toUpperCase());
// string
// 7
// MOZILLA

string
7
MOZILLA

const lines = [];
lines.push("appCodeName: " + navigator.appCodeName);
lines.push("userAgent starts: " + navigator.userAgent.slice(0, 24) + "…");
lines.push(
  "appCodeName alone identifies brand? " +
    (navigator.appCodeName !== "Mozilla" ? "maybe" : "no")
);
console.log(lines.join("\n"));

appCodeName: Mozilla
userAgent starts: Mozilla/5.0 (Windows NT …
appCodeName alone identifies brand? no

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

appCodeName: Mozilla (ignore for sniffing)
geolocation API: available
serviceWorker: available
(exact API lines depend on your browser)

🚀 Common Use Cases

• Learning Navigator — first read-only string properties on navigator.
• Reading legacy code — understand why old scripts check for Mozilla.
• Teaching anti-patterns — show why sniffing with appCodeName fails.
• Not for production branching — do not gate features on this value.
• Debugging myths — prove Chrome still reports Mozilla here.

📝 Notes

• Always "Mozilla" — not a real product name.
• Kept only for compatibility with old content.
• Do not use for browser or engine detection.
• Baseline Widely available across modern browsers.
• Related: appName, activeVRDisplays, Window, JavaScript hub.

💡 Best Practices