Following examples are adopted from Martin Honnen’s blog. Also see namespaces in JS object conversion page.

Default Namespace

A default namespace declaration attribute can be specified as follows:

const { create } = require('xmlbuilder2');

const ns1 = 'http://example.com/ns1';
const doc = create()
  .ele(ns1, 'root')
    .ele(ns1, 'foo').txt('bar').doc();

const xmlString = doc.end({ headless: true });
console.log(xmlString);

which would result in the following:

<root xmlns="http://example.com/ns1"><foo>bar</foo></root>

Namespace Declaration Attribute

A namespace declaration attribute can be specified as follows:

const { create } = require('xmlbuilder2');

const ns1 = 'http://example.com/ns1'
const xsi = 'http://www.w3.org/2001/XMLSchema-instance'

const doc = create().ele(ns1, 'root')
  .att(xsi, 'xsi:schemaLocation', 'http://example.com/n1 schema.xsd')
  .ele(ns1, 'foo').txt('bar').doc()

const xmlString = doc.end({ headless: true, prettyPrint: true });
console.log(xmlString);

which would result in the following:

<root xmlns="http://example.com/ns1"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://example.com/n1 schema.xsd">
 <foo xmlns="">bar</foo>
</root>

Element with Namespace

An element with a namespace declaration can be specified as follows:

const { create } = require('xmlbuilder2');

const svgNs = 'http://www.w3.org/2000/svg'
const xlinkNs = 'http://www.w3.org/1999/xlink'

const doc = create().ele(svgNs, 'svg')
  .att('http://www.w3.org/2000/xmlns/', 'xmlns:xlink', xlinkNs)
  .ele(svgNs, 'script')
    .att('type', 'text/ecmascript')
    .att(xlinkNs, 'xlink:href', 'foo.js')
  .doc()

const xmlString = doc.end({ headless: true, prettyPrint: true });
console.log(xmlString);

which would result in the following:

<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
  <script xmlns="" type="text/ecmascript" xlink:href="foo.js"/>
</svg>

Attribute with Namespace

An attribute with a namespace declaration can be specified as follows:

const { create } = require('xmlbuilder2');

const ns1 = 'http://example.com/ns1'
const doc = create()
  .ele('root').att(ns1, 'att', 'val').doc()

const xmlString = doc.end({ headless: true, prettyPrint: true });
console.log(xmlString);

which would result in the following:

<root xmlns:ns1="http://example.com/ns1" ns1:att="val"/>

Namespace Defaults

xmlbuilder2 can automatically insert namespace defaults for all element and attributes. This is especially useful for MathML and SVG documents. For example, to create the yin and yang SVG:

const { create } = require('xmlbuilder2');

const svgDoc = create({ defaultNamespace: { ele: 'http://www.w3.org/2000/svg', att: null } });
// all svg elements below will be created in the 'http://www.w3.org/2000/svg' namespace
// all attributes will be created with the null namespace
svgDoc.ele('svg').att('viewBox', '0 0 100 100')
  .ele('circle').att({ cx: 50, cy: 50, r: 48, fill: 'none', stroke: '#000' }).up()
  .ele('path').att('d', 'M50,2a48,48 0 1 1 0,96a24 24 0 1 1 0-48a24 24 0 1 0 0-48').up()
  .ele('circle').att({ cx: 50, cy: 26, r: 6 }).up()
  .ele('circle').att({ cx: 50, cy: 74, r: 6, fill: '#FFF' }).up();
console.log(svgDoc.end({ prettyPrint: true }));

which would result in the following:

<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <circle cx="50" cy="50" r="48" fill="none" stroke="#000"/>
  <path d="M50,2a48,48 0 1 1 0,96a24 24 0 1 1 0-48a24 24 0 1 0 0-48"/>
  <circle cx="50" cy="26" r="6"/>
  <circle cx="50" cy="74" r="6" fill="#FFF"/>
</svg>

Namespace Aliases

Namespace aliases can be used instead of actual namespaces by prepending them with the '@' character. The following well-known namespaces are built-in and can be used without being declared:

html: 'http://www.w3.org/1999/xhtml'
xml: 'http://www.w3.org/XML/1998/namespace'
xmlns: 'http://www.w3.org/2000/xmlns/'
mathml: 'http://www.w3.org/1998/Math/MathML'
svg: 'http://www.w3.org/2000/svg'
xlink: 'http://www.w3.org/1999/xlink'

For example:

const { create } = require('xmlbuilder2');

const ele = create().ele('@xml', 'root').att('@xml', 'att', 'val');
console.log(ele.toString()); // '<xml:root xml:att='val'/>'

Custom aliases can be declared while calling the create function:

const { create } = require('xmlbuilder2');

const ele = create({ namespaceAlias: { ns: 'ns1' } }).ele('@ns', 'p:root').att('@ns', 'p:att', 'val')
console.log(ele.toString()); // '<p:root xmlns:p='ns1' p:att='val'/>'

Namespace aliases can also be used while converting JS objects. In that case, element name and alias should be separated by '@@':

const { create } = require('xmlbuilder2');

const ele = create().ele({ 'root@@xml': { '@att@@xml': 'val' }})
console.log(ele.toString()); // '<xml:root xml:att='val'/>'

Namespace Inheritance

Child element nodes automatically inherit their parent element’s namespace. For example:

const { create } = require('xmlbuilder2');

const root = create()
  .ele('http:/example.com', 'root')
    .ele('node')
  .up();
const node = root.node.firstElementChild;
console.log(node.namespaceURI); // 'http:/example.com'