xml2js

What is xml2js?

The xml2js npm package is a library that allows users to convert XML data into a JavaScript object and vice versa. It is useful for working with XML data in a JavaScript environment, such as Node.js applications, where JSON is the more commonly used data format.

What are xml2js's main functionalities?

Parsing XML to JavaScript Object

This feature allows you to parse XML data and convert it into a JavaScript object. The 'parseString' method takes an XML string and a callback function that receives the parsed result.

const xml2js = require('xml2js');
const parser = new xml2js.Parser();
const xml = '<root>Hello xml2js!</root>';

parser.parseString(xml, (err, result) => {
  console.log(result);
});

Converting JavaScript Object to XML

This feature enables you to take a JavaScript object and convert it into an XML string. The 'Builder' class is used to create an XML string from the provided object.

const xml2js = require('xml2js');
const builder = new xml2js.Builder();
const obj = { root: 'Hello xml2js!' };

const xml = builder.buildObject(obj);
console.log(xml);

Customizing Parser Options

xml2js allows you to customize the behavior of the parser through various options. In this example, 'explicitArray' is set to false to avoid wrapping single elements in an array, and 'trim' is set to true to trim the whitespace from the text nodes.

const xml2js = require('xml2js');
const parser = new xml2js.Parser({
  explicitArray: false,
  trim: true
});
const xml = '<root>    Hello xml2js!    </root>';

parser.parseString(xml, (err, result) => {
  console.log(result);
});

Other packages similar to xml2js

fast-xml-parser

fast-xml-parser is an npm package that provides similar XML parsing and building functionalities as xml2js. It is known for its speed and offers a variety of options for parsing, including the ability to validate XML. It can be a faster alternative to xml2js for large XML files or performance-critical applications.

libxmljs

libxmljs is a Node.js package that binds to the libxml C library. It provides XML parsing and serialization, XPath support, and schema validation. Compared to xml2js, libxmljs is a lower-level library that may offer better performance and more advanced XML processing features but with a more complex API.

xmldom

xmldom is a W3C standard-compliant DOM parser and serializer for Node.js. It allows you to manipulate XML documents with a DOM API. While xml2js focuses on converting between XML and JavaScript objects, xmldom is more about providing a DOM interface for XML documents, which can be more familiar to developers with experience in web development.

README

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(data).then(function (result) {
  console.dir(result);
  console.log('Done');
})
.catch(function (err) {
  // Failed
});

// Without parser
xml2js.parseStringPromise(data /*, 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.Parser per 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);

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);

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 when options.normalize is set to true)

• 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.: the xmlns prefix 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: $): Prefix that is used to access the attributes. Version 0.1 default was @.
• charkey (default: _): Prefix that is used to access the character content. Version 0.1 default was #.
• explicitCharkey (default: false)
• trim (default: false): Trim the whitespace at the beginning and end of text nodes.
• normalizeTags (default: false): Normalize all tag names to lowercase.
• normalize (default: false): Trim whitespaces inside text nodes.
• explicitRoot (default: true): Set this if you want to get the root node in the resulting object.
• emptyTag (default: ''): what will the value of empty nodes be.
• explicitArray (default: true): Always put child nodes in an array if true; otherwise an array is created only if there is more than one.
• ignoreAttrs (default: false): Ignore all XML attributes and only create text nodes.
• mergeAttrs (default: false): Merge attributes and child elements as properties of the parent, instead of keying attributes off a child attribute object. This option is ignored if ignoreAttrs is true.
• validator (default null): You can specify a callable that validates the resulting structure somehow, however you want. See unit tests for an example.
• xmlns (default false): Give each element a field usually called '$ns' (the first character is the same as attrkey) that contains its local name and namespace URI.
• explicitChildren (default false): Put child elements to separate property. Doesn't work with mergeAttrs = 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 if explicitChildren is set to true. Added in 0.2.5.
• preserveChildrenOrder (default false): Modifies the behavior of explicitChildren so that the value of the "children" property becomes an ordered array. When this is true, every node will also get a #name field 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 (default false): Determines whether chars should be considered children if explicitChildren is on. Added in 0.2.5.
• includeWhiteChars (default false): Determines whether whitespace-only text nodes should be included. Added in 0.4.17.
• async (default false): Should the callbacks be async? This might be an incompatible change if your code depends on sync execution of callbacks. Future versions of xml2js might change this default, so the recommendation is to not depend on sync execution anyway. Added in 0.2.6.
• strict (default true): Set sax-js to strict or non-strict parsing mode. Defaults to true which 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 an Array of functions with following signature:

  function (name){
      //do something with `name`
      return name
  }
  

  Added in 0.4.14
• attrValueProcessors (default: null): Allows the addition of attribute value processing functions. Accepts an Array of functions with following signature:

  function (value, name){
    //do something with `name`
    return name
  }
  

  Added in 0.4.1
• tagNameProcessors (default: null): Allows the addition of tag name processing functions. Accepts an Array of functions with following signature:

  function (name){
    //do something with `name`
    return name
  }
  

  Added in 0.4.1
• valueProcessors (default: null): Allows the addition of element value processing functions. Accepts an Array of functions with following signature:

  function (value, name){
    //do something with `name`
    return name
  }
  

  Added in 0.4.6

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 (default root or the root key name): root element name to be used in case explicitRoot is false or 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.version A version number string, e.g. 1.0
  • xmldec.encoding Encoding declaration, e.g. UTF-8
  • xmldec.standalone standalone document declaration: true or false
• doctype (default null): 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.