ECMAscript for XML

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Draft

ECMAscript for XML (ak E4X) is an extension to ECMAscript.

It is available in

Using E4X is considerably simpler than using the DOM. Maybe some day we will be back to the elegance of languages like LISP instead of fighting against obscure C/Java syntax. But for now there are two problems with E4X: (1) It can't read the DOM, in otherwords you only can manipulate XML as (external) data. (2) There seem to be some inconsistencies that developers complain about.

Overview

Usage patterns

Example XML code

In most examples, we will use the following XML fragment, i.e. instructions will refer to the following XML fragment. It is also available as instructions-empty.xml. Test code is instructions-e4x.xhtml (XHTML-capable Browser needed, IE will not work as of Nov 2008) 

instructions=<stepbystep>
  <doctitle>Sample document</doctitle>
  <info>
    <para>
     See <a href="http://edutechwiki.unige.ch/en/ECMAscript_for_XML"
            name="hot_link">ECMAscript for XML</a></para>
  </info>
  <steps>
    <title>List of steps</title>
    <step>
      <title status="draft">Step 1</title>
      <para>Think !</para>
    </step>
    <step id="s2">
      <title>Step 2</title>
    </step>
    <step id="s3">
      <title>Step 3</title>
      <para>That was easy !</para>
    </step>
  </steps>
</stepbystep>;


Creating an E4X XML object

(1) Using the XML literal syntax

The easiest way is to create a new variable and just create the XML structure like this. In ECMAScript 4 (e.g. ActionScript 3) you should define the type of the variable. 

var instructions:XML  = <stepbystep>
  <doctitle></doctitle>
  <steps>
    <title></title>
  </steps>
 </stepbystep>;

Don't forget the ";" at the end since this instruction extends over several lines.

(1b) In JavaScript 1.6 (ECMAScript 3) you can't define types and you simply use: 

 var instructions  = <stepbystep> ....

This the same principle as creating an array or an object like this: 

 var arr = [item1,item2,item3];
 var obj = {a:"item 1",b:"item 2",c:"item 3"}
Using the XML constructor

(2) You also can create an XML E4X object from a string with the new XML() constructor.

var instruction_string = "<stepbystep> 

 <doctitle></doctitle>
 <steps>
   <title></title>
 </steps>
</stepbystep>";

var instruction2:XML = new XML(instruction_string);

(3) Dynamic values Using the XML literal syntax is very practical when you want to create markup dynamically.

Variables and expressions can be used to create XML contents by simply wrapping them with braces ({}). Note: To create attribute values, omit the quotation marks (as in the example below)! 

var URL = "http://edutechwiki.unige.ch/en/ECMAscript_for_XML";
var URL_text = "ECMAscript for XML";
var A   = <a href={URL}>{URL_text}</a>;

The value of A is: 

 <a href="http://edutechwiki.unige.ch/en/ECMAscript_for_XML">ECMAscript for XML</a>

XML lists

XML lists are the other important datastructure in E4X. Lists are needed for example to hold results of queries (like NodeLists in the DOM model).

Here is a little example of an XML list: 

    <step>
      <title>step 1</title>
    </step>
    <step>
      <title>step 2</title>
    </step>
    <step>
      <title>step 3</title>
    </step>


Accessing elements and attributes

There is a similarity between E4X objects, arrays, and traditional Object.

(1) Getting en element with the "." operator

To access an element you simply can use an expression like a.b.c to walk down the tree. The result is either an XML fragment or an XMLList depending on whether there is only one child or several children.

  • Extracting a list of elements:
 var step_list = instructions.steps.step;
Result, i.e. step_list is now:
 <step> <title>step 1</title> </step>
 <step> <title>step 2</title></step>
 <step> <title>step 3</title>  <para>That was easy !</para></step>
(2) Extracting precise elements with the [] operator
  • Extracting element 0 of element 2
 var para = instructions.steps.step[2].para[0];
Result, i.e. para is:
 <para>That was easy !</para>
(3) Extracting descendants with the ".." operator
  • To extract descendants use the
 var grandchild = instructions..para;
Result, grandchild is:
 <para> See <a href="http://edutechwiki.unige.ch/en/ECMAscript_for_XML">ECMAscript for XML</a>
 </para><para>That was easy !</para>
(4) Getting en attribute with the "@" operator
 var attr = instructions..a.@href;
Result, attr is:
 http://edutechwiki.unige.ch/en/ECMAscript_for_XML

About namespaces

E4X can handle namespaces: E.g. to extract an xlink:href attribute in the following kind of fragment: xml = <STORY> 

       <INFOS>
   	<a xmlns:xlink="http://www.w3.org/1999/xlink"

xlink:href="http://edutechwiki.unige.ch/en/ECMAscript_for_XML">ECMAscript for XML</a> </INFOS> 

   </STORY>;

You will have to define a Namespace object 

 var NS = new Namespace("http://www.w3.org/1999/xlink");

and then use the variable as prefix 

 @NS::href;

function show_URL() {
      var NS = new Namespace("http://www.w3.org/1999/xlink");
      var URL = xml..a;
      var link = URL.@NS::href;
      alert ("URL (content of the 'a' tag)=" + URL + "\n" + "NameSpace=" + NS + "\nxlink:href=" + link);
      }

List of methods

XML Objects

Retrieving nodes and attributes

attribute(attributeName)
Returns an XMLList with 0 or 1 XML attributes associated with this XML object that have the given attributeName.
attributes()
returns an XMLList containing the XML attributes of an object
Example:
 instructions.info..a.attributes()
Returns:
 http://edutechwiki.unige.ch/en/ECMAscript_for_XML
 hot_line
child(propertyName)
returns the list of children in this XML object matching the given propertyName
This is equivalent to using child.propertyName.
 var x = instructions.child("steps");
 var y = instructions.steps;
x==y above
children()
Returns an XMLList with all the children
 instructions.children()
descendants([name])
returns all the XML valued descendants (children, grandchildren, great-grandchildren, etc.) of this XML object with the given name. If the name parameter is omitted, it returns all descendants of this XML object.
Example
 instructions.descendants("para")
Same as
 instructions..para
elements([name])
returns an XMLList containing all the children of this XML object that are XML elements with the given name. When the elements method is called with no parameters, it returns an XMLList containing all the children of this XML object that are XML elements

Names and Namespaces

localName()
returns the local name portion of the qualified name of this XML object, i.e. the element or attribute name without namespace prefix.
name ()
returns the qualified name associated with this XML object.

Counting

childIndex()
Returns the index number (ordinal position starting at 1) with respect to parent context.
Example
 instructions..step[2].childIndex())
Returns
 3
length()
Always returns 1

Changing nodes and attributes

appendChild(child)
Adds a child at the end of a XMLList and returns this list. It also modifies the whole XML fragment of course.
Exampleinstructions.info..a.attributes()
 var new1 = instructions.steps.appendChild(<step><title>step 4</title>
     <para>New contents appended !</para></step>);
Result returned is the new list of child objects
 <steps>
 <title>List of steps</title>
   ..........
 <step><title>step 3</title><para>That was easy !</para></step>
 <step><title>step 4</title> <para>New contents appended !</para> </step>
 </steps>
insertChildAfter(child1, child2)
inserts the given child2 after the given child1 in this XML object and returns this XML object. If child1 is null, the insertChildAfter method inserts child2 before all children of this XML object (i.e., after none of them). If child1 does not exist in this XML object, it returns without modifying this XML object.
insertChildBefore(child1, child2)

inserts the given child2 before the given child1 in this XML object and returns this XML object. If child1 is null, the insertChildBefore method inserts child2 after all children in this XML object (i.e., before none of them). If child1 does not exist in this XML object, it returns without modifying this XML object.


name()
normalize()
parent()


processingInstructions([name])
comments()
returns an XMLList with all the comments
prependChild(value)
contains(value)
returns the result of comparing this XML object with the given value
Example
 var xmlnode = instructions..step[0].title;
 append_text_string("contains()", xmlnode.contains("Step 1"));
Returns
 true
removeNamespace(namespace)
copy()
returns a deep copy of this XML object with the internal Parent property set to null
replace(propertyName, value)

Tests

hasComplexContent()
returns a true or flase indicating whether this XML object contains complex content, i.e. child elements. Note: attributes, comments, PIs and text nodes cannot have complex content.
hasSimpleContent()
returns true or false indicating whether this XML object contains simple content, i.e. if it is a text node, an attribute node or an XML element without child elements.
inScopeNamespaces()
returns an Array of Namespace objects representing the namespaces in scope for this XML object in the context of its parent

(to do)

namespace([prefix])
namespaceDeclarations()
addNamespace(namespace)
setChildren(value)
nodeKind()
setLocalName(name)
setName(name)
setNamespace(ns)
text()
toString()
toXMLString()
valueOf()


XML List objects

Other stuff

attribute(attributeName)
attributes()
child(propertyName)
normalize()
parent()
children()
processingInstructions([name])
comments()
contains(value)
copy()
descendants([name])
elements([name])
hasComplexContent()
hasSimpleContent()
text()
toString()
toXMLString()
length()
valueOf()


Examples used

  • Story (look at the source of this file)

Links

Overviews

Introductions and tutorials

JavaScript
  • E4X by Mark. Useful as short manual !
Flash/ActionScript/Flex
  • E4X (Adobe, Flex, Getting Started)
Php
Namespaces
Ajax
  • Fremantle, Paul and Anthony Elder (1005). AJAX and scripting Web services with E4X, Part 1, IBM Works, HTML

Standard and Manuals

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