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.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);

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 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: $): Prefix that is used to access the attributes.
  Version 0.1 default was @.
• charkey (default: _): Prefix that is used to access the character
  content. Version 0.1 default was #.
• explicitCharkey (default: false) Determines whether or not to use
  a charkey prefix for elements with no attributes.
• trim (default: false): Trim the whitespace at the beginning and end of
  text nodes.
• normalizeTags (default: false): Normalize all tag names to lowercase.
• normalize (default: false): Trim whitespaces inside text nodes.
• explicitRoot (default: true): Set this if you want to get the root
  node in the resulting object.
• emptyTag (default: ''): what will the value of empty nodes be. In case
  you want to use an empty object as a default value, it is better to provide a factory
  function () => ({}) instead. Without this function a plain object would
  become a shared reference across all occurrences with unwanted behavior.
• explicitArray (default: true): Always put child nodes in an array if
  true; otherwise an array is created only if there is more than one.
• ignoreAttrs (default: false): Ignore all XML attributes and only create
  text nodes.
• mergeAttrs (default: false): Merge attributes and child elements as
  properties of the parent, instead of keying attributes off a child
  attribute object. This option is ignored if ignoreAttrs is true.
• validator (default null): You can specify a callable that validates
  the resulting structure somehow, however you want. See unit tests
  for an example.
• xmlns (default false): Give each element a field usually called ‘$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.