fast-xml-parser

To customize XML parsing, instantiate the XMLParser class with an options object. By default, attributes are ignored unless ignoreAttributes: false is specified.

const {XMLParser} = require('fast-xml-parser');

const options = {
    ignoreAttributes : false
};

const parser = new XMLParser(options);
let jsonObj = parser.parse(xmlDataStr);

You can install fast-xml-parser as a project dependency using npm or yarn, or install it globally to use it as a system command.

To use it in a Node.js project:

$ npm install fast-xml-parser
# or
$ yarn add fast-xml-parser

To use it as a system command:

$ npm install fast-xml-parser -g

To use it on a webpage, include it via a CDN.

Fast XML Parser supports Processing Instructions (PI tags), but treats them as normal tags during parsing. To ensure attributes within PI tags are processed correctly, you must set ignoreAttributes: false and allowBooleanAttributes: true in your parser options.

Note the following behavior:

• PI tag names start with a ? character.
• The #text property is always empty to maintain consistency with other parsed properties.
• Attributes are parsed using the same logic as normal tags.

const options = {
    ignoreAttributes: false,
    format: true,
    preserveOrder: true,
    allowBooleanAttributes: true
};
const parser = new XMLParser(options);
let result = parser.parse(xmlData);

To use the library in an HTML page, include the minified script from a CDN and access the classes via the fxparser global object.

<script src="path/to/fxp.min.js"></script>
<script>
  const parser = new fxparser.XMLParser();
  parser.parse(xmlContent);
</script>

To reconstruct XML containing Processing Instructions from a parsed JS ordered object, use XMLBuilder with the following configuration:

• ignoreAttributes: false
• preserveOrder: true
• allowBooleanAttributes: true
• suppressBooleanAttributes: true (optional, used to clean up boolean attribute output)

This ensures that PI tags (starting with ?) and their attributes are correctly formatted in the output XML.

const options = {
    ignoreAttributes: false,
    preserveOrder: true,
    allowBooleanAttributes: true,
    suppressBooleanAttributes: true
};
const builder = new XMLBuilder(options);
const output = builder.build(result);

You can run the benchmarks using the following commands:

• All Benchmarks: Runs the entire benchmark suite.
• Parser Benchmarks: Runs only the parser-specific benchmarks.
• Builder Benchmarks: Runs only the builder-specific benchmarks.

When using jPath: false and Expression objects in callbacks, always pre-compile your expressions outside of the callback. Creating a new Expression() inside a callback is extremely slow as it parses the pattern for every single node processed.

// ✅ GOOD - Parse once, reuse many times
const expr = new Expression("..user[id]");

const parser = new XMLParser({
  stopNodes: [expr],
  jPath: false,
  tagValueProcessor: (tagName, val, matcher) => {
    if (matcher.matches(expr)) {
      // Fast matching - expression already parsed
    }
    return val;
  }
});

// ❌ BAD - Parse on every callback
const parser = new XMLParser({
  jPath: false,
  tagValueProcessor: (tagName, val, matcher) => {
    // Slow - creates new Expression every time
    if (matcher.matches(new Expression("..user[id]"))) {
      // ...
    }
    return val;
  }
});

The XMLBuilder functionality has been moved from the fast-xml-parser package to a dedicated standalone package called fast-xml-builder. To avoid bugs affecting the parser and to ensure future compatibility, you should migrate your imports. XMLBuilder will be removed from the fast-xml-parser package in the next major version.

// From
import { XMLBuilder } from "fast-xml-parser";

// To
import XMLBuilder from "fast-xml-builder";