XML Processing Strategies in JavaScript Applications
These libraries handle XML data in JavaScript, but they serve different roles. Some focus on parsing XML into JSON objects, others build XML from scratch, and some provide a DOM interface similar to browsers. fast-xml-parser and xml2js convert XML to JSON for easy manipulation. xmlbuilder specializes in generating XML structures. xmldom offers a DOM API for XML. libxmljs and libxmljs2 use native bindings for high performance but require Node.js. Choosing the right tool depends on whether you need speed, browser support, or DOM compatibility.
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XML Processing in JavaScript: Parsers, Builders, and DOM Implementations
Working with XML in JavaScript requires choosing between speed, compatibility, and API style. The six packages here cover three main areas: parsing XML into data, building XML from data, and manipulating XML via DOM methods. Some rely on native code for performance, while others run purely in JavaScript. Let's compare how they handle real-world tasks.
⚙️ Parsing Engine: Native Bindings vs Pure JavaScript
The core difference lies in how these libraries process XML. Native bindings offer speed but limit where you can run your code. Pure JavaScript works everywhere but may be slower on massive files.
libxmljs uses native C++ bindings to libxml2.
- Requires compilation via node-gyp.
- Fails in browsers or serverless environments without specific binaries.
// libxmljs: Native parsing
const libxmljs = require("libxmljs");
const xmlDoc = libxmljs.parseXmlString('<root><item>1</item></root>');
console.log(xmlDoc.toString());
libxmljs2 is a maintained fork of libxmljs.
- Same native requirements as the original.
- Better long-term support for Node.js versions.
// libxmljs2: Native parsing (fork)
const libxmljs2 = require("libxmljs2");
const xmlDoc = libxmljs2.parseXmlString('<root><item>1</item></root>');
console.log(xmlDoc.toString());
fast-xml-parser is written entirely in JavaScript.
- No compilation needed.
- Runs in browsers, Node.js, and Deno.
// fast-xml-parser: Pure JS parsing
const { XMLParser } = require("fast-xml-parser");
const parser = new XMLParser();
const result = parser.parse('<root><item>1</item></root>');
console.log(result);
xml2js is also pure JavaScript.
- Very stable and widely adopted.
- Uses callbacks by default but supports promises.
// xml2js: Pure JS parsing
const { parseStringPromise } = require("xml2js");
const result = await parseStringPromise('<root><item>1</item></root>');
console.log(result);
xmldom provides a DOM parser in pure JavaScript.
- Mimics browser
DOMParser. - Deprecated in favor of
@xmldom/xmldom.
// xmldom: DOM parsing
const { DOMParser } = require("xmldom");
const doc = new DOMParser().parseFromString('<root><item>1</item></root>', 'text/xml');
console.log(doc.toString());
📦 Data Output: JSON Objects vs DOM Trees
How you access data matters. JSON is easier for JavaScript logic. DOM trees allow XPath and node traversal.
fast-xml-parser converts XML directly to JSON objects.
- Attributes and tags become properties.
- Easy to integrate with modern app state.
// fast-xml-parser: JSON output
const parser = new XMLParser();
const json = parser.parse('<user id="1">Alice</user>');
// { user: { "@_id": "1", "#text": "Alice" } }
xml2js also outputs JSON but with a different structure.
- Often wraps text in arrays.
- Configurable via options.
// xml2js: JSON output
const result = await parseStringPromise('<user id="1">Alice</user>');
// { user: { $: { id: "1" }, _: "Alice" } }
xmldom returns a DOM tree.
- Use
getElementsByTagNameto find nodes. - Closer to browser API but heavier.
// xmldom: DOM output
const doc = new DOMParser().parseFromString('<user id="1">Alice</user>', 'text/xml');
const node = doc.getElementsByTagName('user')[0];
console.log(node.getAttribute('id'));
libxmljs and libxmljs2 return native DOM-like objects.
- Support XPath queries directly.
- Faster for complex queries on large documents.
// libxmljs2: XPath query
const xmlDoc = libxmljs2.parseXmlString('<root><item id="1"/></root>');
const nodes = xmlDoc.findall('//item[@id]');
console.log(nodes.length);
🛠️ Building XML: Generation Tools
Some projects need to create XML, not just read it. Dedicated builders simplify this task.
xmlbuilder is designed specifically for creating XML.
- Chainable API for nodes and attributes.
- Does not parse existing XML.
// xmlbuilder: Creating XML
const builder = require("xmlbuilder");
const xml = builder.create('root')
.ele('item', { id: "1" }).txt('Value').up()
.end();
fast-xml-parser includes a builder component.
- Converts JSON back to XML.
- Keeps parsing and building in one package.
// fast-xml-parser: Building from JSON
const { XMLBuilder } = require("fast-xml-parser");
const builder = new XMLBuilder();
const xml = builder.build({ root: { item: "Value" } });
xml2js also has a Builder class.
- Complements its parser.
- Useful if you already use
xml2jsfor parsing.
// xml2js: Building from JSON
const { Builder } = require("xml2js");
const builder = new Builder();
const xml = builder.buildObject({ root: { item: "Value" } });
⚠️ Maintenance and Security Status
Security and active maintenance are critical for XML libraries due to vulnerabilities like XXE.
xmldom is officially deprecated.
- The npm page advises using
@xmldom/xmldom. - Security fixes may not land in the unscoped version.
// xmldom: Deprecation warning
// Do not use in new projects. Switch to @xmldom/xmldom.
libxmljs has had periods of low activity.
- Native dependencies can break with Node updates.
libxmljs2is the recommended fork for stability.
// libxmljs vs libxmljs2
// Prefer libxmljs2 for ongoing Node.js compatibility.
fast-xml-parser and xml2js are actively maintained.
- Pure JS means fewer breakages during Node upgrades.
- Regular security patches for parsing logic.
// fast-xml-parser & xml2js
// Both are safe choices for long-term projects.
📊 Summary: Capabilities at a Glance
| Package | Environment | Output Type | Building Support | Maintenance |
|---|---|---|---|---|
fast-xml-parser | Any (Pure JS) | JSON | ✅ Yes | ✅ Active |
libxmljs | Node (Native) | DOM/XPath | ❌ No | ⚠️ Stalled |
libxmljs2 | Node (Native) | DOM/XPath | ❌ No | ✅ Active Fork |
xml2js | Any (Pure JS) | JSON | ✅ Yes | ✅ Active |
xmlbuilder | Any (Pure JS) | XML String | ✅ Yes (Only) | ✅ Active |
xmldom | Any (Pure JS) | DOM | ❌ No | ❌ Deprecated |
💡 Final Recommendation
fast-xml-parser is the best all-rounder for modern apps. It handles parsing and building with high speed and no native dependencies. Use it for APIs, configuration files, and data exchange.
xml2js is a solid alternative if you need legacy compatibility. It is stable and well-understood, though slightly slower than fast-xml-parser.
libxmljs2 is the choice for heavy server-side workloads. Use it if you need XPath or native performance and can guarantee a Node.js environment.
xmlbuilder shines when generating complex XML documents. Pair it with a parser if you need round-trip support.
xmldom should be avoided. Switch to @xmldom/xmldom if you strictly need DOM methods in JavaScript.
Final Thought: For most frontend and full-stack developers, pure JavaScript solutions like fast-xml-parser offer the best balance of safety, speed, and deployment flexibility.
How to Choose: xml2js vs fast-xml-parser vs libxmljs vs libxmljs2 vs xmlbuilder vs xmldom
- xml2js:
Choose
xml2jsfor stable, proven XML-to-JSON conversion in Node.js or bundled web apps. It has been around for years and handles most standard XML structures reliably. The API is callback-based but supports promises. It is a safe default for legacy systems or projects prioritizing stability over raw speed. - fast-xml-parser:
Choose
fast-xml-parserwhen you need high performance in a pure JavaScript environment. It handles both parsing and building without native dependencies, making it safe for browsers and serverless functions. It supports validation and complex XML features like attributes and tags. This is ideal for modern APIs where speed and security matter. - libxmljs:
Choose
libxmljsonly if you are locked into a Node.js environment and require native libxml2 features. Be aware that it requires compilation and may fail on systems without build tools. It is not suitable for frontend or serverless deployments. Considerlibxmljs2instead for better maintenance support. - libxmljs2:
Choose
libxmljs2if you need native XML processing in Node.js but want a more actively maintained fork. It offers the same performance benefits aslibxmljswith fewer stagnation risks. Like its predecessor, it cannot run in browsers due to native bindings. Use this for heavy-duty server-side XML workflows. - xmlbuilder:
Choose
xmlbuilderwhen your primary task is generating XML documents from JavaScript objects. It provides a clean chainable API for constructing nodes and attributes. It does not focus on parsing, so pair it with a parser if you need bidirectional support. This is best for creating feeds, sitemaps, or SOAP requests. - xmldom:
Avoid
xmldomfor new projects as it is deprecated in favor of@xmldom/xmldom. It mimics the browser DOM API for XML, which is useful for XPath or DOM manipulation. If you must use it, know that security patches may be delayed. Only select this if you strictly require DOM methods in a Node environment.
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README for xml2js
node-xml2js
Ever had the urge to parse XML? And wanted to access the data in some sane, easy way? Don't want to compile a C parser, for whatever reason? Then xml2js is what you're looking for!
Description
Simple XML to JavaScript object converter. It supports bi-directional conversion. Uses sax-js and xmlbuilder-js.
Note: If you're looking for a full DOM parser, you probably want JSDom.
Installation
Simplest way to install xml2js is to use npm, just npm install xml2js which will download xml2js and all dependencies.
xml2js is also available via Bower, just bower install xml2js which will download xml2js and all dependencies.
Usage
No extensive tutorials required because you are a smart developer! The task of parsing XML should be an easy one, so let's make it so! Here's some examples.
Shoot-and-forget usage
You want to parse XML as simple and easy as possible? It's dangerous to go alone, take this:
var parseString = require('xml2js').parseString;
var xml = "<root>Hello xml2js!</root>"
parseString(xml, function (err, result) {
console.dir(result);
});
Can't get easier than this, right? This works starting with xml2js 0.2.3.
With CoffeeScript it looks like this:
{parseString} = require 'xml2js'
xml = "<root>Hello xml2js!</root>"
parseString xml, (err, result) ->
console.dir result
If you need some special options, fear not, xml2js supports a number of
options (see below), you can specify these as second argument:
parseString(xml, {trim: true}, function (err, result) {
});
Simple as pie usage
That's right, if you have been using xml-simple or a home-grown wrapper, this was added in 0.1.11 just for you:
var fs = require('fs'),
xml2js = require('xml2js');
var parser = new xml2js.Parser();
fs.readFile(__dirname + '/foo.xml', function(err, data) {
parser.parseString(data, function (err, result) {
console.dir(result);
console.log('Done');
});
});
Look ma, no event listeners!
You can also use xml2js from
CoffeeScript, further reducing
the clutter:
fs = require 'fs',
xml2js = require 'xml2js'
parser = new xml2js.Parser()
fs.readFile __dirname + '/foo.xml', (err, data) ->
parser.parseString data, (err, result) ->
console.dir result
console.log 'Done.'
But what happens if you forget the new keyword to create a new Parser? In
the middle of a nightly coding session, it might get lost, after all. Worry
not, we got you covered! Starting with 0.2.8 you can also leave it out, in
which case xml2js will helpfully add it for you, no bad surprises and
inexplicable bugs!
Promise usage
var xml2js = require('xml2js');
var xml = '<foo></foo>';
// With parser
var parser = new xml2js.Parser(/* options */);
parser.parseStringPromise(xml).then(function (result) {
console.dir(result);
console.log('Done');
})
.catch(function (err) {
// Failed
});
// Without parser
xml2js.parseStringPromise(xml /*, options */).then(function (result) {
console.dir(result);
console.log('Done');
})
.catch(function (err) {
// Failed
});
Parsing multiple files
If you want to parse multiple files, you have multiple possibilities:
- You can create one
xml2js.Parserper file. That's the recommended one and is promised to always just work. - You can call
reset()on your parser object. - You can hope everything goes well anyway. This behaviour is not guaranteed work always, if ever. Use option #1 if possible. Thanks!
So you wanna some JSON?
Just wrap the result object in a call to JSON.stringify like this
JSON.stringify(result). You get a string containing the JSON representation
of the parsed object that you can feed to JSON-hungry consumers.
Displaying results
You might wonder why, using console.dir or console.log the output at some
level is only [Object]. Don't worry, this is not because xml2js got lazy.
That's because Node uses util.inspect to convert the object into strings and
that function stops after depth=2 which is a bit low for most XML.
To display the whole deal, you can use console.log(util.inspect(result, false, null)), which displays the whole result.
So much for that, but what if you use
eyes for nice colored output and it
truncates the output with …? Don't fear, there's also a solution for that,
you just need to increase the maxLength limit by creating a custom inspector
var inspect = require('eyes').inspector({maxLength: false}) and then you can
easily inspect(result).
XML builder usage
Since 0.4.0, objects can be also be used to build XML:
var xml2js = require('xml2js');
var obj = {name: "Super", Surname: "Man", age: 23};
var builder = new xml2js.Builder();
var xml = builder.buildObject(obj);
will result in:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root>
<name>Super</name>
<Surname>Man</Surname>
<age>23</age>
</root>
At the moment, a one to one bi-directional conversion is guaranteed only for
default configuration, except for attrkey, charkey and explicitArray options
you can redefine to your taste. Writing CDATA is supported via setting the cdata
option to true.
To specify attributes:
var xml2js = require('xml2js');
var obj = {root: {$: {id: "my id"}, _: "my inner text"}};
var builder = new xml2js.Builder();
var xml = builder.buildObject(obj);
will result in:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root id="my id">my inner text</root>
Adding xmlns attributes
You can generate XML that declares XML namespace prefix / URI pairs with xmlns attributes.
Example declaring a default namespace on the root element:
let obj = {
Foo: {
$: {
"xmlns": "http://foo.com"
}
}
};
Result of buildObject(obj):
<Foo xmlns="http://foo.com"/>
Example declaring non-default namespaces on non-root elements:
let obj = {
'foo:Foo': {
$: {
'xmlns:foo': 'http://foo.com'
},
'bar:Bar': {
$: {
'xmlns:bar': 'http://bar.com'
}
}
}
}
Result of buildObject(obj):
<foo:Foo xmlns:foo="http://foo.com">
<bar:Bar xmlns:bar="http://bar.com"/>
</foo:Foo>
Processing attribute, tag names and values
Since 0.4.1 you can optionally provide the parser with attribute name and tag name processors as well as element value processors (Since 0.4.14, you can also optionally provide the parser with attribute value processors):
function nameToUpperCase(name){
return name.toUpperCase();
}
//transform all attribute and tag names and values to uppercase
parseString(xml, {
tagNameProcessors: [nameToUpperCase],
attrNameProcessors: [nameToUpperCase],
valueProcessors: [nameToUpperCase],
attrValueProcessors: [nameToUpperCase]},
function (err, result) {
// processed data
});
The tagNameProcessors and attrNameProcessors options
accept an Array of functions with the following signature:
function (name){
//do something with `name`
return name
}
The attrValueProcessors and valueProcessors options
accept an Array of functions with the following signature:
function (value, name) {
//`name` will be the node name or attribute name
//do something with `value`, (optionally) dependent on the node/attr name
return value
}
Some processors are provided out-of-the-box and can be found in lib/processors.js:
-
normalize: transforms the name to lowercase. (Automatically used whenoptions.normalizeis set totrue) -
firstCharLowerCase: transforms the first character to lower case. E.g. 'MyTagName' becomes 'myTagName' -
stripPrefix: strips the xml namespace prefix. E.g<foo:Bar/>will become 'Bar'. (N.B.: thexmlnsprefix is NOT stripped.) -
parseNumbers: parses integer-like strings as integers and float-like strings as floats E.g. "0" becomes 0 and "15.56" becomes 15.56 -
parseBooleans: parses boolean-like strings to booleans E.g. "true" becomes true and "False" becomes false
Options
Apart from the default settings, there are a number of options that can be
specified for the parser. Options are specified by new Parser({optionName: value}). Possible options are:
attrkey(default:$): Prefix that is used to access the attributes. Version 0.1 default was@.charkey(default:_): Prefix that is used to access the character content. Version 0.1 default was#.explicitCharkey(default:false) Determines whether or not to use acharkeyprefix for elements with no attributes.trim(default:false): Trim the whitespace at the beginning and end of text nodes.normalizeTags(default:false): Normalize all tag names to lowercase.normalize(default:false): Trim whitespaces inside text nodes.explicitRoot(default:true): Set this if you want to get the root node in the resulting object.emptyTag(default:''): what will the value of empty nodes be. In case you want to use an empty object as a default value, it is better to provide a factory function() => ({})instead. Without this function a plain object would become a shared reference across all occurrences with unwanted behavior.explicitArray(default:true): Always put child nodes in an array if true; otherwise an array is created only if there is more than one.ignoreAttrs(default:false): Ignore all XML attributes and only create text nodes.mergeAttrs(default:false): Merge attributes and child elements as properties of the parent, instead of keying attributes off a child attribute object. This option is ignored ifignoreAttrsistrue.validator(defaultnull): You can specify a callable that validates the resulting structure somehow, however you want. See unit tests for an example.xmlns(defaultfalse): Give each element a field usually called '$ns' (the first character is the same as attrkey) that contains its local name and namespace URI.explicitChildren(defaultfalse): Put child elements to separate property. Doesn't work withmergeAttrs = true. If element has no children then "children" won't be created. Added in 0.2.5.childkey(default$$): Prefix that is used to access child elements ifexplicitChildrenis set totrue. Added in 0.2.5.preserveChildrenOrder(defaultfalse): Modifies the behavior ofexplicitChildrenso that the value of the "children" property becomes an ordered array. When this istrue, every node will also get a#namefield whose value will correspond to the XML nodeName, so that you may iterate the "children" array and still be able to determine node names. The named (and potentially unordered) properties are also retained in this configuration at the same level as the ordered "children" array. Added in 0.4.9.charsAsChildren(defaultfalse): Determines whether chars should be considered children ifexplicitChildrenis on. Added in 0.2.5.includeWhiteChars(defaultfalse): Determines whether whitespace-only text nodes should be included. Added in 0.4.17.async(defaultfalse): Should the callbacks be async? This might be an incompatible change if your code depends on sync execution of callbacks. Future versions ofxml2jsmight change this default, so the recommendation is to not depend on sync execution anyway. Added in 0.2.6.strict(defaulttrue): Set sax-js to strict or non-strict parsing mode. Defaults totruewhich is highly recommended, since parsing HTML which is not well-formed XML might yield just about anything. Added in 0.2.7.attrNameProcessors(default:null): Allows the addition of attribute name processing functions. Accepts anArrayof functions with following signature:
Added in 0.4.14function (name){ //do something with `name` return name }attrValueProcessors(default:null): Allows the addition of attribute value processing functions. Accepts anArrayof functions with following signature:
Added in 0.4.1function (value, name){ //do something with `name` return name }tagNameProcessors(default:null): Allows the addition of tag name processing functions. Accepts anArrayof functions with following signature:
Added in 0.4.1function (name){ //do something with `name` return name }valueProcessors(default:null): Allows the addition of element value processing functions. Accepts anArrayof functions with following signature:
Added in 0.4.6function (value, name){ //do something with `name` return name }
Options for the Builder class
These options are specified by new Builder({optionName: value}).
Possible options are:
attrkey(default:$): Prefix that is used to access the attributes. Version 0.1 default was@.charkey(default:_): Prefix that is used to access the character content. Version 0.1 default was#.rootName(defaultrootor the root key name): root element name to be used in caseexplicitRootisfalseor to override the root element name.renderOpts(default{ 'pretty': true, 'indent': ' ', 'newline': '\n' }): Rendering options for xmlbuilder-js.- pretty: prettify generated XML
- indent: whitespace for indentation (only when pretty)
- newline: newline char (only when pretty)
xmldec(default{ 'version': '1.0', 'encoding': 'UTF-8', 'standalone': true }: XML declaration attributes.xmldec.versionA version number string, e.g. 1.0xmldec.encodingEncoding declaration, e.g. UTF-8xmldec.standalonestandalone document declaration: true or false
doctype(defaultnull): optional DTD. Eg.{'ext': 'hello.dtd'}headless(default:false): omit the XML header. Added in 0.4.3.allowSurrogateChars(default:false): allows using characters from the Unicode surrogate blocks.cdata(default:false): wrap text nodes in<![CDATA[ ... ]]>instead of escaping when necessary. Does not add<![CDATA[ ... ]]>if it is not required. Added in 0.4.5.
renderOpts, xmldec,doctype and headless pass through to
xmlbuilder-js.
Updating to new version
Version 0.2 changed the default parsing settings, but version 0.1.14 introduced the default settings for version 0.2, so these settings can be tried before the migration.
var xml2js = require('xml2js');
var parser = new xml2js.Parser(xml2js.defaults["0.2"]);
To get the 0.1 defaults in version 0.2 you can just use
xml2js.defaults["0.1"] in the same place. This provides you with enough time
to migrate to the saner way of parsing in xml2js 0.2. We try to make the
migration as simple and gentle as possible, but some breakage cannot be
avoided.
So, what exactly did change and why? In 0.2 we changed some defaults to parse
the XML in a more universal and sane way. So we disabled normalize and trim
so xml2js does not cut out any text content. You can reenable this at will of
course. A more important change is that we return the root tag in the resulting
JavaScript structure via the explicitRoot setting, so you need to access the
first element. This is useful for anybody who wants to know what the root node
is and preserves more information. The last major change was to enable
explicitArray, so everytime it is possible that one might embed more than one
sub-tag into a tag, xml2js >= 0.2 returns an array even if the array just
includes one element. This is useful when dealing with APIs that return
variable amounts of subtags.
Running tests, development
The development requirements are handled by npm, you just need to install them.
We also have a number of unit tests, they can be run using npm test directly
from the project root. This runs zap to discover all the tests and execute
them.
If you like to contribute, keep in mind that xml2js is written in
CoffeeScript, so don't develop on the JavaScript files that are checked into
the repository for convenience reasons. Also, please write some unit test to
check your behaviour and if it is some user-facing thing, add some
documentation to this README, so people will know it exists. Thanks in advance!
Getting support
Please, if you have a problem with the library, first make sure you read this
README. If you read this far, thanks, you're good. Then, please make sure your
problem really is with xml2js. It is? Okay, then I'll look at it. Send me a
mail and we can talk. Please don't open issues, as I don't think that is the
proper forum for support problems. Some problems might as well really be bugs
in xml2js, if so I'll let you know to open an issue instead :)
But if you know you really found a bug, feel free to open an issue instead.