JavaScript Navigator doNotTrack Property

What You’ll Learn

navigator.doNotTrack reflects the user’s old Do Not Track preference ("1", "0", or null). Learn why DNT failed, the values, safer alternatives, five examples, and try-it labs.

Introduction

Do Not Track was meant to be a polite signal: the user asks sites not to track them, and sites voluntarily comply. In practice, many advertising systems ignored the signal.

navigator.doNotTrack exposes that preference in JavaScript (matching the DNT HTTP header). MDN now treats the whole approach as discontinued — ineffective for privacy and potentially harmful as fingerprinting noise.

Understanding the doNotTrack Property

Think of doNotTrack as a historical preference flag — not an enforceable lock against trackers.

• "1" — user requests not to be tracked (DNT enabled).
• "0" — user opted in to tracking (per MDN’s example notes).
• null — no preference / unset in many browsers.
• HTTP twin — same idea as the DNT request header.
• Why it failed — cooperative only; ignored by many trackers; added fingerprint bits.

📝 Syntax

General form of the property:

navigator.doNotTrack

Value

• A string ("1" or "0") or null.

Common patterns (legacy / learning only)

// MDN-style log (do not rely on this for privacy):
console.log(navigator.doNotTrack);
// "1" if DNT enabled; "0" if opted-in; otherwise null

// Prefer modern signals when available:
if (navigator.globalPrivacyControl === true) {
  // User has Global Privacy Control enabled (where supported)
}

Examples Gallery

Examples follow MDN navigator.doNotTrack patterns for learning. Prefer Try It Yourself to inspect your browser. Do not treat these checks as a complete privacy solution.

console.log(navigator.doNotTrack);
// prints "1" if DNT is enabled; "0" if opted-in; otherwise null

null
(or "1" / "0" depending on browser settings)

function dntLabel(value) {
  if (value === "1") return "DNT: request no tracking";
  if (value === "0") return "DNT: opted in to tracking";
  return "DNT: unset / null";
}

console.log(dntLabel(navigator.doNotTrack));

DNT: unset / null

const v = navigator.doNotTrack;
const lines = [
  "value: " + String(v),
  "typeof: " + typeof v
];
console.log(lines.join("\n"));

value: null
typeof: object
(null is typeof "object" in JavaScript)

// Legacy pattern — NOT recommended for new apps
function legacyShouldReduceTracking() {
  return navigator.doNotTrack === "1";
}

console.log(
  "legacy reduce tracking?: " + legacyShouldReduceTracking()
);

legacy reduce tracking?: false
(true only when doNotTrack is exactly "1")

function privacySignals() {
  return {
    doNotTrack: navigator.doNotTrack, // deprecated — diagnostic only
    globalPrivacyControl:
      typeof navigator.globalPrivacyControl === "boolean"
        ? navigator.globalPrivacyControl
        : "unsupported",
    advice: "Do not rely on DNT for new privacy logic"
  };
}

console.log(JSON.stringify(privacySignals()));

{"doNotTrack":null,"globalPrivacyControl":"unsupported","advice":"Do not rely on DNT for new privacy logic"}
(GPC may be true/false where supported)

🚀 Common Use Cases

• Learning / interviews — explain why cooperative DNT failed.
• Legacy audits — find old doNotTrack === "1" branches to remove.
• Support diagnostics — log the value only with other privacy signals.
• Migration — replace DNT checks with GPC + consent tooling.
• Not for new tracking gates — DNT alone is not a compliance strategy.

📝 Notes

• Deprecated and Non-standard on MDN — do not use in new production privacy logic.
• Values are "1", "0", or null.
• DNT was cooperative; many trackers ignored it.
• MDN warns DNT can increase fingerprinting surface.
• Related: globalPrivacyControl, geolocation, JavaScript hub.

💡 Best Practices