XSLT-processor

A JavaScript XSLT processor without native library dependencies.

Interactive Demos

Try the XSLT and XPath processors directly in your browser:

🚀 Visit Interactive Demos

How to

Install xslt-processor using npm, ohpm or yarn:

npm install xslt-processor

ohpm install xslt-processor

yarn add xslt-processor

Within your ES2015+ code, import the Xslt class, the XmlParser class and use this way:

import { Xslt, XmlParser } from 'xslt-processor'

// xmlString: string of xml file contents
// xsltString: string of xslt file contents
// outXmlString: output xml string.
const xslt = new Xslt();
const xmlParser = new XmlParser();
// Either
const outXmlString = await xslt.xsltProcess(
	xmlParser.xmlParse(xmlString),
	xmlParser.xmlParse(xsltString)
);
// Or
xslt.xsltProcess(
	xmlParser.xmlParse(xmlString),
	xmlParser.xmlParse(xsltString)
).then(output => {
  // `output` is equivalent to `outXmlString` (a string with XML).
});

If you write pre-2015 JS code, make adjustments as needed.

Xslt class options

You can pass an options object to Xslt class:

const options = {
  escape: false,
  selfClosingTags: true,
  parameters: [{ name: 'myparam', value: '123' }],
  outputMethod: 'xml'
};
const xslt = new Xslt(options);

• cData (boolean, default true): resolves CDATA elements in the output. Content under CDATA is resolved as text. This overrides escape for CDATA content.
• escape (boolean, default true): replaces symbols like <, >, & and " by the corresponding HTML/XML entities. Can be overridden by disable-output-escaping, that also does the opposite, unescaping > and < by < and >, respectively.
• selfClosingTags (boolean, default true): Self-closes tags that don't have inner elements, if true. For instance, <test></test> becomes <test />.
• outputMethod (string, default xml): Specifies the default output method. if <xsl:output> is declared in your XSLT file, this will be overridden. Valid values: xml, html, text, name, xhtml, json, adaptive.
• parameters (array, default []): external parameters that you want to use.
  • name: the parameter name;
  • namespaceUri (optional): the namespace;
  • value: the value.

JSON Output Format

When using outputMethod: 'json', the XSLT processor will convert the resulting XML document to JSON format. This is useful for APIs and modern JavaScript applications.

Example:

const xslt = new Xslt({ outputMethod: 'json' });
const xmlParser = new XmlParser();

const xmlString = `<root>
  <users>
    <user>Alice</user>
    <user>Bob</user>
  </users>
</root>`;

const xsltString = `<?xml version="1.0"?>
  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
      <xsl:copy-of select="root"/>
    </xsl:template>
  </xsl:stylesheet>`;

const result = await xslt.xsltProcess(
  xmlParser.xmlParse(xmlString),
  xmlParser.xmlParse(xsltString)
);

// result will be a JSON string:
// {"root":{"users":{"user":["Alice","Bob"]}}}

const parsed = JSON.parse(result);
console.log(parsed.root.users.user); // ["Alice", "Bob"]

JSON Structure Rules:

• Each element becomes a property in a JSON object
• Text-only elements become string values
• Elements with multiple children of the same name become arrays
• Empty elements are omitted from the output
• Attributes are prefixed with @ (when present in the output)
• Mixed text and element content uses the #text property for text nodes

Adaptive Output Format

When using outputMethod: 'adaptive', the XSLT processor automatically detects the most appropriate output format based on the transformation result. This implements XSLT 3.1 adaptive output behavior.

Detection Rules:

• If the output contains only text nodes (no elements), it returns as plain text
• If the output contains one or more elements, it returns as XML

Example:

const xslt = new Xslt({ outputMethod: 'adaptive' });
const xmlParser = new XmlParser();

// Example 1: Pure text output
const xmlString1 = `<root><value>Hello World</value></root>`;
const xsltString1 = `<?xml version="1.0"?>
  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
      <xsl:value-of select="root/value"/>
    </xsl:template>
  </xsl:stylesheet>`;

const result1 = await xslt.xsltProcess(
  xmlParser.xmlParse(xmlString1),
  xmlParser.xmlParse(xsltString1)
);
console.log(result1); // "Hello World" (plain text)

// Example 2: XML output
const xmlString2 = `<root><user>John</user></root>`;
const xsltString2 = `<?xml version="1.0"?>
  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
      <users><xsl:copy-of select="root/user"/></users>
    </xsl:template>
  </xsl:stylesheet>`;

const result2 = await xslt.xsltProcess(
  xmlParser.xmlParse(xmlString2),
  xmlParser.xmlParse(xsltString2)
);
console.log(result2); // "<users><user>John</user></users>" (XML)

Direct use in browsers

You can simply add a tag like this:

<script type="application/javascript" src="https://www.unpkg.com/xslt-processor@latest/umd/xslt-processor.global.js"></script>

All the exports will live under globalThis.XsltProcessor and window.XsltProcessor. See a usage example here.

XPath Parser

To access the XPath parser, you can use the instance present at Xslt class:

const xslt = new Xslt();
const xPath = xslt.xPath;

Or you can import it like this:

import { XPath } from 'xslt-processor'

const xPath = new XPath();

XPath class is an external dependency, living in its own repository.

Introduction

XSLT-processor contains an implementation of XSLT in JavaScript. Because XSLT uses XPath, it also contains an implementation of XPath that can be used independently of XSLT. This implementation has the advantage that it makes XSLT uniformly available whenever the browser's native XSLTProcessor() is not available such as in Node.js or in web workers.

XSLT-processor builds on Google's AJAXSLT which was written before XSLTProcessor() became available in browsers, but the code base has been updated to comply with ES2015+ and to make it work outside of browsers.

This implementation of XSLT operates at the DOM level on its input documents. It internally uses a DOM implementation to create the output document, but usually returns the output document as text stream. The DOM to construct the output document can be supplied by the application, or else an internal minimal DOM implementation is used. This DOM comes with a minimal XML parser that can be used to generate a suitable DOM representation of the input documents if they are present as text.

Tests and usage examples

New tests are written in Jest an can be run by calling: yarn test.

The files xslt.html and xpath.html in the directory interactive-tests are interactive tests. They can be run directly from the file system; no HTTP server is needed.

Both interactive tests and automatic tests demonstrate the use of the library functions.

Conformance

A few features that are required by the XSLT and XPath standards were left out (but patches to add them are welcome).

See our TODO for a list of missing features that we are aware of (please add more items by means of PRs).

So far, we have implemented XQuery functions for versions 1.0 and 2.0, but this is not complete yet.

The DOM implementation is minimal so as to support the XSLT processing, and not intended to be complete.

The implementation is all agnostic about namespaces. It just expects XSLT elements to have tags that carry the xsl: prefix, but we disregard all namespace declaration for them.

There are a few nonstandard XPath functions.

HTML Conformance

HTML per se is not strict XML. Because of that, starting on version 2.0.0, this library handles HTML differently than XML:

• For a document to be treated as HTML, it needs to have a <!DOCTYPE> tag defined with one of the following valid formats:
  • <!DOCTYPE html> (for HTML5);
  • <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> (for HTML4);
  • <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> (for XHTML 1.1).
• Tags like <hr>, <link> and <meta> don't need to be closed. The output for these tags doesn't close them (adding a / before the tag closes, or a corresponding close tag);
  • This rule doesn't apply for XHTML, which is strict XML.

Whitespace Handling

This library supports xsl:strip-space and xsl:preserve-space for controlling whitespace in the input document.

xsl:strip-space

Use <xsl:strip-space> to remove whitespace-only text nodes from specified elements in the input document:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <!-- Strip whitespace from all elements -->
    <xsl:strip-space elements="*"/>

    <!-- Or strip from specific elements -->
    <xsl:strip-space elements="book chapter section"/>

    <!-- ... templates ... -->
</xsl:stylesheet>

The elements attribute accepts:

• * - matches all elements
• name - matches elements with the specified local name
• prefix:* - matches all elements in a namespace
• prefix:name - matches a specific element in a namespace
• Multiple patterns separated by whitespace (e.g., "book chapter section")

xsl:preserve-space

Use <xsl:preserve-space> to preserve whitespace in specific elements, overriding xsl:strip-space:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:strip-space elements="*"/>
    <!-- Preserve whitespace in pre and code elements -->
    <xsl:preserve-space elements="pre code"/>

    <!-- ... templates ... -->
</xsl:stylesheet>

Precedence Rules

1. xml:space="preserve" attribute on an element takes highest precedence
2. xsl:preserve-space overrides xsl:strip-space for matching elements
3. xsl:strip-space applies to remaining matches
4. By default (no declarations), whitespace is preserved

Breaking Changes

Breaking changes are usually documented at every major release, but we also keep a short version of them below.

Version 2

Until version 2.3.1, use like the example below:

import { Xslt, XmlParser } from 'xslt-processor'

// xmlString: string of xml file contents
// xsltString: string of xslt file contents
// outXmlString: output xml string.
const xslt = new Xslt();
const xmlParser = new XmlParser();
const outXmlString = xslt.xsltProcess( // Not async.
	xmlParser.xmlParse(xmlString),
	xmlParser.xmlParse(xsltString)
);

Version 3 received <xsl:include> which relies on Fetch API, which is asynchronous. Version 2 doesn't support <xsl:include>.

If using Node.js older than version v17.5.0, please use version 3.2.3, that uses node-fetch package. Versions 3.3.0 onward require at least Node.js version v17.5.0, since they use native fetch() function.

Version 1

Until version 1.2.8, use like the example below:

import { Xslt, xmlParse } from 'xslt-processor'

// xmlString: string of xml file contents
// xsltString: string of xslt file contents
// outXmlString: output xml string.
const xslt = new Xslt();
const outXmlString = xslt.xsltProcess(
	xmlParse(xmlString),
	xmlParse(xsltString)
);

Version 0

Until version 0.11.7, use like the example below:

import { xsltProcess, xmlParse } from 'xslt-processor'

// xmlString: string of xml file contents
// xsltString: string of xslt file contents
// outXmlString: output xml string.
const outXmlString = xsltProcess(
	xmlParse(xmlString),
	xmlParse(xsltString)
);

and to access the XPath parser:

import { xpathParse } from 'xslt-processor'

These functions are part of Xslt and XPath classes, respectively, at version 1.x onward.

References

• XPath Specification: http://www.w3.org/TR/1999/REC-xpath-19991116
• XSLT Specification: http://www.w3.org/TR/1999/REC-xslt-19991116
• W3C DOM Level 3 Core Specification: http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407/
• ECMAScript Language Specification: http://www.ecma-international.org/publications/standards/Ecma-262.htm
• Arkts Language Specification: https://gitee.com/openharmony/arkcompiler_runtime_core/releases/download/ArkTS-spec-1.2.0-alpha-20250307/arktsspecification.pdf