The Web platform provides the following objects for parsing and serializing XML:
- XMLSerializer to serialize DOM trees to strings
- XPath to address (point to) different parts of an XML document (through a non-XML syntax) into strings
- DOMParser to parse XML from strings into DOM trees
- XMLHttpRequest to parse URL-addressable resources into DOM trees
Part 1: how to create an XML document
In this section, we create an XML document (which is an instance of Document) starting from different points.
Parsing strings into DOM trees
Building an XML document starting from a JavaScript Object tree (JXON)
Please see the JXON reverse algorithms.
Parsing URL-addressable resources into DOM trees
Using XMLHttpRequest
Here is sample code that reads and parses a URL-addressable XML file into a DOM tree:
var xhr = new XMLHttpRequest();
xhr.onload = function() {
dump(xhr.responseXML.documentElement.nodeName);
}
xhr.onerror = function() {
dump("Error while getting XML.");
}
xhr.open("GET", "example.xml");
xhr.responseType = "document";
xhr.send();
xhr.responseXML is a Document instance.
node.js
If you prefer node.js, this code also parses a file into a DOM tree. Unlike XMLHttpRequest, it does not work with remote files:
var oFile = DirIO.get("ProfD"); // %Profile% dir
oFile.append("extensions");
oFile.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}");
oFile.append("people.xml");
oDOM = (new DOMParser()).parseFromString(FileIO.read(oFile), "text/xml");
// print the name of the root element or error message
dump(oDOM.documentElement.nodeName == "parsererror" ? "error while parsing" : oDOM.documentElement.nodeName);
Part 2: how to serialize the content of a given XML document
In this section we already have a parsed XML document (that is, an instance of {{ domxref("Document") }}) and want to use its content.
Serializing DOM trees to strings
First, create a DOM tree as described in How to Create a DOM tree. Alternatively, use a DOM tree obtained from {{ domxref("XMLHttpRequest") }}.
Now, let's serialize doc — the DOM tree — to a string:
var oSerializer = new XMLSerializer(); var sXML = oSerializer.serializeToString(doc);
From within a JS XPCOM component (or a JS module), new XMLSerializer() is not available. Instead, write:
var oSerializer = Components.classes["@mozilla.org/xmlextras/xmlserializer;1"] .createInstance(Components.interfaces.nsIDOMSerializer); var sXML = oSerializer.serializeToString(doc);
"Pretty" serialization of DOM trees to strings
You can pretty print a DOM tree using XMLSerializer and E4X. First, create a DOM tree as described in the How to Create a DOM tree article. Alternatively, use a DOM tree obtained from {{ domxref("XMLHttpRequest") }}. We assume it's in the doc variable.
var oSerializer = new XMLSerializer(); var sPrettyXML = XML(oSerializer.serializeToString(doc)).toXMLString();
Indents are provided with two spaces. You can use {{ domxref("treeWalker") }} to write a more efficient version and customize the indent string.
toXMLString method, your CDATA elements will be lost, and only the containing text will remain. So if you have CDATA elements in your XML, using the preceding method might not be useful.<content><![CDATA[This is the content]]></content>
Becomes
<content>This is the content</content>
Serializing DOM trees to Javascript Object trees (JXON)
JXON (lossless JavaScript XML Object Notation) is a generic name by which is defined the representation of JavaScript Objects using XML. If you are interested in addressing only some parts of an XML document, use XPath instead of converting the whole document into JSON! Otherwise, read the article about JXON.
Serializing DOM trees to files
First, create a DOM tree as described in the How to Create a DOM tree article. If you already have a DOM tree from using {{ domxref("XMLHttpRequest") }}, skip to the end of this section.
Now, let's serialize doc — the DOM tree — to a file (you can read more about using files in Mozilla):
var oFOStream = Components.classes["@mozilla.org/network/file-output-stream;1"].createInstance(Components.interfaces.nsIFileOutputStream);
var oFile = Components.classes["@mozilla.org/file/directory_service;1"].getService(Components.interfaces.nsIProperties).get("ProfD", Components.interfaces.nsILocalFile); // get profile folder
oFile.append("extensions"); // extensions sub-directory
oFile.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}"); // GUID of your extension
oFile.append("myXMLFile.xml"); // filename
oFOStream.init(oFile, 0x02 | 0x08 | 0x20, 0664, 0); // write, create, truncate
(new XMLSerializer()).serializeToStream(doc, oFOStream, ""); // rememeber, doc is the DOM tree
oFOStream.close();
Serializing XMLHttpRequest objects to files
If you already have a DOM tree from using {{ domxref("XMLHttpRequest") }}, use the same code as above but replace serializer.serializeToStream(doc, oFOStream, "") with serializer.serializeToStream(xmlHttpRequest.responseXML.documentElement, oFOStream, "") where xmlHttpRequest is an instance of XMLHttpRequest.
Note that this first parses the XML retrieved from the server, then re-serializes it into a stream. Depending on your needs, you could just save the xmlHttpRequest.responseText directly.
See also
{{ languages( {"ja": "ja/Parsing_and_serializing_XML","zh-cn": "zh-cn/Parsing_and_serializing_XML", "it": "it/Costruire_e_decostruire_un_documento_XML" } ) }}