@nodable/flexible-xml-parser

A high-performance, flexible XML parser in pure javascript for Node.js and browsers with pluggable output builders, composable value parsers, and multiple input modes.

From the creater of fast-xml-parser

Benefits over fast-xml-parser?

Feature	fast-xml-parser	flexible-xml-parser
Output format	Fixed JS object	Pluggable (compact, sequential, node-tree, custom)
Value parsing	Inline options	Separate, composable pipeline per output builder
Value parsers for tags vs attrs	Single config	Independent chains
Input modes	String / Buffer	String, Buffer, Uint8Array, Stream, Feed/End
Stop node enclosures	Limited	Per-node skipEnclosures control
Exit	After complete processing	Allow partial parsing
Lenient HTML mode	No	autoClose with error collection
Custom output	No	Extend BaseOutputBuilder

The core parser is intentionally minimal. Options like transformTagName, alwaysArray, forceTextNode, and value parser configuration live in the output builder, not in XMLParser. This keeps the parser lean and lets you mix builders without changing your parsing code.

Performance

fast-xml-parser doesn't support streams, while flexible-xml-parser does. This makes flexible-xml-parser more memory efficient for large XML files.

Additionally, flexible-xml-parser is considerably faster than fast-xml-parser. Checkout benchmarks for more details.

Package Ecosystem

@nodable/flexible-xml-parser is the core parser. Output builders are published separately so you only install what you need:

Package	Description
@nodable/flexible-xml-parser	Core parser (this package)
@nodable/base-output-builder	Base class + value parsers (ElementType, entity parsers)
@nodable/compact-builder	Default JS-object output (like fast-xml-parser)
@nodable/sequential-builder	Ordered key-value array output
@nodable/sequential-stream-builder	Sequential builder with streaming output
@nodable/node-tree-builder	Uniform AST-style node tree

Installation

npm install @nodable/flexible-xml-parser @nodable/compact-builder

Install additional builders only as needed.

Quick Start

import XMLParser from '@nodable/flexible-xml-parser';
import { CompactBuilderFactory } from '@nodable/compact-builder';

// Default output (uses CompactBuilder internally)
const parser = new XMLParser();
const result = parser.parse('<root><count>3</count><active>true</active></root>');
// { root: { count: 3, active: true } }

// With attributes
const parser2 = new XMLParser({ skip: { attributes: false } });
parser2.parse('<item id="1">hello</item>');
// { item: { '@_id': 1, '#text': 'hello' } }

Options

All options are optional. Pass only what you need.

new XMLParser({
  // What to skip
  skip: {
    attributes:  true,   // Skip all attributes
    declaration: false,  // Skip <?xml ...?> declaration
    pi:          false,  // Skip <?...?> processing instructions
    cdata:       false,  // Exclude CDATA from output entirely
    comment:     false,  // Exclude comments from output entirely
    nsPrefix:    false,  // Strip namespace prefixes (ns:tag → tag)
    tags:        [],     // Tag paths to drop silently from output
  },

  // Property names for special nodes
  nameFor: {
    text:    '#text',  // mixed-content text property
    cdata:   '',       // '' = merge into text; '#cdata' = separate key
    comment: '',       // '' = omit; '#comment' = capture
  },

  // Attribute representation
  attributes: {
    prefix:      '@_',
    suffix:      '',
    groupBy:     '',     // group all attributes under this key; '' = inline
    booleanType: false,  // allow valueless attributes (treated as true)
  },

  // Tag options
  tags: {
    unpaired:  [],  // self-closing tags without / (e.g. ['br', 'img'])
    stopNodes: [],  // paths whose content is captured raw (see docs/04-stop-nodes.md)
  },

  // DoS prevention
  limits: {
    maxNestedTags:       null,
    maxAttributesPerTag: null,
  },

  // DOCTYPE entity expansion
  doctypeOptions: {
    enabled:        false,
    maxEntityCount: 100,
    maxEntitySize:  10000,
  },

  // Security
  strictReservedNames:   false,
  onDangerousProperty:   defaultOnDangerousProperty,

  // Stop parsing early based on a condition
  exitIf: null,

  // Buffer settings for feed/stream modes
  feedable: {
    maxBufferSize:  10 * 1024 * 1024,
    autoFlush:      true,
    flushThreshold: 1024,
  },

  // Lenient HTML-mode recovery
  autoClose: null,  // null = strict; 'html' = recover from unclosed/mismatched tags

  // Pluggable output builder
  OutputBuilder: null,  // default: CompactBuilder
});

Value Parsers

Value parsers are configured on the output builder, not on XMLParser. This lets you set independent pipelines for tag text and attribute values.

Built-in parsers: 'entity', 'number', 'boolean', 'trim', 'currency'.

import { CompactBuilderFactory } from '@nodable/compact-builder';

const builder = new CompactBuilderFactory({
  tags:       { valueParsers: ['entity', 'boolean', 'number'] },
  attributes: { valueParsers: ['entity', 'number', 'boolean'] },
});

const parser = new XMLParser({ OutputBuilder: builder });

See docs/03-value-parsers.md for the full pipeline reference and custom parser guide.

Input Modes

// String or Buffer
parser.parse('<root/>');
parser.parse(Buffer.from('<root/>'));

// Typed array
parser.parseBytesArr(new Uint8Array([...]));

// Node.js Readable stream
const result = await parser.parseStream(fs.createReadStream('large.xml'));

// Incremental feed (WebSocket, chunked HTTP, etc.)
parser.feed('<root>');
parser.feed('<item>1</item>');
const result = parser.end();

Possible Usage

• Parse XML config files, SOAP responses, RSS/Atom feeds
• Stream-parse large XML files with bounded memory
• Build custom AST-style output with NodeTreeBuilder
• Lenient HTML-fragment parsing with autoClose
• Stop-node capture for <script>, <style>, embedded HTML
• Extend BaseOutputBuilder to write parsed data directly to a database

Documentation

File	Topic
docs/01-getting-started.md	Installation, quick start, common patterns
docs/02-options.md	Full options reference
docs/03-value-parsers.md	Value parser pipeline, built-ins, custom parsers
docs/04-stop-nodes.md	Stop nodes and skip tags
docs/05-output-builders.md	Built-in and custom output builders
docs/06-streaming.md	Stream, feed/end, and memory characteristics
docs/07-auto-close.md	Lenient HTML parsing and error collection
docs/08-security.md	Security, DoS limits, prototype pollution
docs/09-path-expressions.md	Path expression syntax for stop nodes, skip, exitIf
docs/10-typescript.md	TypeScript usage and type definitions

License

MIT — Amit Gupta