JavaScript Document xmlEncoding Property

What You’ll Learn

Document.xmlEncoding is a deprecated read-only instance property that reported encoding from the XML declaration. Learn when it returns null, MDN’s UTF-16 example, how it differs from characterSet, and five examples with try-it labs.

Introduction

XML files can start with a declaration such as <?xml version="1.0" encoding="UTF-16"?>. That encoding attribute tells parsers which character encoding the bytes use.

MDN: Document.xmlEncoding returned the encoding as determined by the XML declaration. It should be null if unspecified or unknown. MDN warns not to use this attribute—it was removed from DOM Level 4 and dropped in Firefox 10.0.

Related Document tutorials: characterSet, contentType, Document constructor.

Understanding Document.xmlEncoding

A read-only instance property from the legacy DOM XML era.

• Value — encoding string from XML declaration (MDN), e.g. "UTF-16".
• null — when encoding is unspecified or unknown (MDN).
• HTML documents — usually null (no XML declaration).
• Read-only — you cannot assign a new encoding here.
• Deprecated — removed from DOM Level 4; not in Firefox 10+ (MDN).

📝 Syntax

document.xmlEncoding

Value

A string or null (MDN).

MDN XML declaration example

<?xml version="1.0" encoding="UTF-16"?>
<!-- document.xmlEncoding would be "UTF-16" on legacy XML docs -->

⚖️ xmlEncoding vs characterSet vs contentType

Examples Gallery

Examples follow MDN Document: xmlEncoding. On HTML try-it pages, expect null in modern browsers.

console.log(document.xmlEncoding);
// Typical HTML page in modern browsers: null

null

<?xml version="1.0" encoding="UTF-16"?>
<root/>

// Legacy XML document (MDN example):
console.log(document.xmlEncoding); // "UTF-16"

UTF-16

console.log({
  xmlEncoding: document.xmlEncoding,
  characterSet: document.characterSet
});
// Typical: { xmlEncoding: null, characterSet: "UTF-8" }

{ xmlEncoding: null, characterSet: "UTF-8" }

function getDocumentEncoding() {
  if ("xmlEncoding" in document && document.xmlEncoding !== null) {
    return document.xmlEncoding; // legacy path
  }
  return document.characterSet; // modern path
}

console.log(getDocumentEncoding());

UTF-8

const encoding = document.characterSet;
const isUtf8 = encoding.toUpperCase().replace(/_/g, "-") === "UTF-8";

console.log({ encoding, isUtf8 });

{ encoding: "UTF-8", isUtf8: true }

🚀 Why This Property Existed

• Legacy XML documents — read declaration encoding from the DOM (historical).
• Migration audits — find xmlEncoding reads and replace with characterSet.
• Old tutorials — understand pre-DOM4 encoding APIs.
• Not for HTML — use <meta charset> and characterSet.
• Not for new XML — parse XML with DOMParser or fetch bytes + decode explicitly.
• Firefox note — removed since Firefox 10.0 (MDN).

📝 Notes

• MDN: Deprecated — do not use; removed from DOM Level 4.
• Firefox: not supported since version 10.0 (MDN warning).
• Returns null when encoding is unspecified or unknown (MDN).
• HTML pages: prefer document.characterSet and <meta charset="utf-8">.
• Related: characterSet, contentType, visibilityState.

💡 Best Practices