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Parsing and serializing XML

From MDC


Mozilla doesn't support the W3C's Document Object Model Load and Save at this moment (bug 155749), so the easiest way to serialize and deserialize DOM trees is to use the following Mozilla-specific interfaces:

  • XMLSerializer to serialize DOM trees to strings or to files
  • DOMParser to parse XML from strings into DOM trees
  • XMLHttpRequest to parse XML from files into DOM trees. Although DOMParser does have a method named parseFromStream(), it's actually easier to XMLHttpRequest which works for remote (not limited to HTTP) and local files.

Contents

[edit] Serializing DOM trees to strings

First, create a DOM tree as described in How to Create a DOM tree.

Now, let's serialize doc — the DOM tree — to a string: 

var serializer = new XMLSerializer();
var xml = serializer.serializeToString(doc);

[edit] Serializing DOM trees to files

First, create a DOM tree as described in the How to Create a DOM tree article. If you have already have a DOM tree from using 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 serializer = new XMLSerializer();
var foStream = Components.classes["@mozilla.org/network/file-output-stream;1"]
               .createInstance(Components.interfaces.nsIFileOutputStream);
var file = Components.classes["@mozilla.org/file/directory_service;1"]
           .getService(Components.interfaces.nsIProperties)
           .get("ProfD", Components.interfaces.nsIFile); // get profile folder
file.append("extensions");   // extensions sub-directory
file.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}");   // GUID of your extension
file.append("myXMLFile.xml");   // filename
foStream.init(file, 0x02 | 0x08 | 0x20, 0664, 0);   // write, create, truncate
serializer.serializeToStream(doc, foStream, "");   // rememeber, doc is the DOM tree
foStream.close();

[edit] Serializing XMLHttpRequest objects to files

If you already have a DOM tree from using XMLHttpRequest, use the same code as above but replace serializer.serializeToStream(doc, foStream, "") with serializer.serializeToStream(xmlHttpRequest.responseXML.documentElement, foStream, "") 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.

[edit] Parsing strings into DOM trees

var theString='<a id="a"><b id="b">hey!</b></a>';
var parser = new DOMParser();
var dom = parser.parseFromString(theString, "text/xml");
// print the name of the root element or error message
dump(dom.documentElement.nodeName == "parsererror" ? "error while parsing" : dom.documentElement.nodeName);

Tutorial to make this work cross browser

[edit] Parsing files into DOM trees

[edit] XMLHttpRequest

As was previously mentioned, even though DOMParser does have a method named parseFromStream(), it's easier to use XMLHttpRequest to parse XML files into DOM trees (XMLHttpRequest works for both local and remote files). Here is sample code which reads and parses a local XML file into a DOM tree: 

var req = new XMLHttpRequest();
req.open("GET", "chrome://passwdmaker/content/people.xml", false); 
req.send(null);
// print the name of the root element or error message
var dom = req.responseXML;
dump(dom.documentElement.nodeName == "parsererror" ? "error while parsing" : dom.documentElement.nodeName);

req.responseXML is a Document instance.

[edit] io.js

If you prefer io.js, this code will also parse a file into a DOM tree. Unlike XMLHttpRequest, it will not work with remote files: 

var file = DirIO.get("ProfD"); // %Profile% dir
file.append("extensions");
file.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}");
file.append("people.xml");
var fileContents = FileIO.read(file);
var domParser = new DOMParser();
var dom = domParser.parseFromString(fileContents, "text/xml");
// print the name of the root element or error message
dump(dom.documentElement.nodeName == "parsererror" ? "error while parsing" : dom.documentElement.nodeName);

[edit] Resources

  • Sarissa - Sarissa is a cross-browser ECMAScript library for client side XML manipulation, including loading XML from URLs or strings, performing XSLT transformations, XPath queries and more. Supported: Gecko (Mozilla, Firefox etc), IE, KHTML (Konqueror, Safari). If you're writing JavaScript that is used in both XUL applications and HTML pages, and the HTML pages may be viewed in non-Gecko-based applications (such as Internet Explorer, Opera, Konqueror, Safari), you should consider using Sarissa to parse and/or serialize XML. Note: Do not create a DOM object using document.implementation.createDocument() and then use Sarissa classes and methods to manipulate that object. It will not work. You must use Sarissa to create the initial DOM object.
  • Parsing and Serializing XML at XUL Planet
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