From 9ace67d06f2369e3c770e3a11e06e1c8cc9f66fd Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Thu, 15 Jul 2021 12:58:54 -0400 Subject: delete pages that were never translated from en-US (de, part 1) (#1548) --- .../index.html | 412 --------------------- 1 file changed, 412 deletions(-) delete mode 100644 files/de/web/xpath/introduction_to_using_xpath_in_javascript/index.html (limited to 'files/de/web/xpath/introduction_to_using_xpath_in_javascript') diff --git a/files/de/web/xpath/introduction_to_using_xpath_in_javascript/index.html b/files/de/web/xpath/introduction_to_using_xpath_in_javascript/index.html deleted file mode 100644 index 93dc70994e..0000000000 --- a/files/de/web/xpath/introduction_to_using_xpath_in_javascript/index.html +++ /dev/null @@ -1,412 +0,0 @@ ---- -title: Einführung in den Gebrauch von XPath in JavaScript -slug: Web/XPath/Introduction_to_using_XPath_in_JavaScript -translation_of: Web/XPath/Introduction_to_using_XPath_in_JavaScript -original_slug: Web/JavaScript/Einführung_in_den_Gebrauch_von_XPath_in_JavaScript ---- -

Dieses Dokument beschreibt die Schnittstelle zu XPath in JavaScript intern, in Erweiterungen und in Webseiten. Mozilla implementiert einen großen Teil von DOM 3 XPath, sodass XPath auf HTML- und XML-Dokumente angewendet werden kann.

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Die Hauptschnittstelle für die Anwendung von XPath ist die evaluate-Methode des document-Objekts.

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document.evaluate

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Diese Methode wertet  XPath Ausdrücke in Bezug auf ein XML basierendes Dokument (einschließlich HTML-Documente) aus und gibt ein XPathResult-Objekt zurück, das ein Einzelknoten oder eine Zusammenstellung mehrerer Knoten sein kann. Die vorhandene Dokumentation dieser Methode ist unter document.evaluate zu finden, sie ist jedoch für unseren jetzigen Bedarf ziemlich knapp gehalten. Eine umfangreichere Betrachtung wird nachfolgend beschrieben.

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var xpathResult = document.evaluate( xpathExpression, contextNode, namespaceResolver, resultType, result );
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Parameter

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Die evaluate Funktion nimmt insgesamt fünf Parameter entgegen:

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Rückgabewert

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Returns xpathResult, which is an XPathResult object of the type specified in the resultType parameter. The XPathResult Interface is defined {{ Source("dom/interfaces/xpath/nsIDOMXPathResult.idl", "here") }}.

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Einen Standard-Namensraumauflöser (Default Namespace Resolver) implementieren

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Wir erstellen einen Namensraumauflöser mit Hilfe der createNSResolver-Methode des document-Objekts.

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var nsResolver = document.createNSResolver( contextNode.ownerDocument == null ? contextNode.documentElement : contextNode.ownerDocument.documentElement );
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Or alternatively by using the <code>createNSResolver</code> method of a <code>XPathEvaluator</code> object. <pre> var xpEvaluator = new XPathEvaluator(); var nsResolver = xpEvaluator.createNSResolver( contextNode.ownerDocument == null ? contextNode.documentElement : contextNode.ownerDocument.documentElement ); </pre> And then pass document.evaluate, the nsResolver variable as the namespaceResolver parameter.

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Note: XPath defines QNames without a prefix to match only elements in the null namespace. There is no way in XPath to pick up the default namespace as applied to a regular element reference (e.g., p[@id='_myid'] for xmlns='http://www.w3.org/1999/xhtml'). To match default elements in a non-null namespace, you either have to refer to a particular element using a form such as ['namespace-uri()='http://www.w3.org/1999/xhtml' and name()='p' and @id='_myid'] (this approach works well for dynamic XPath's where the namespaces might not be known) or use prefixed name tests, and create a namespace resolver mapping the prefix to the namespace. Read more on how to create a user defined namespace resolver, if you wish to take the latter approach.

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Anmerkungen

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Adapts any DOM node to resolve namespaces so that an XPath expression can be easily evaluated relative to the context of the node where it appeared within the document. This adapter works like the DOM Level 3 method lookupNamespaceURI on nodes in resolving the namespaceURI from a given prefix using the current information available in the node's hierarchy at the time lookupNamespaceURI is called. Also correctly resolves the implicit xml prefix.

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Festlegung des Rückgabetyps

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The returned variable xpathResult from document.evaluate can either be composed of individual nodes (simple types), or a collection of nodes (node-set types).

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Simple Types

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When the desired result type in resultType is specified as either:

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We obtain the returned value of the expression by accessing the following properties respectively of the XPathResult object.

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Beispiel
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The following uses the XPath expression count(//p) to obtain the number of <p> elements in a HTML document:

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var paragraphCount = document.evaluate( 'count(//p)', document, null, XPathResult.ANY_TYPE, null );
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-alert( 'This document contains ' + paragraphCount.numberValue + ' paragraph elements' );
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Although JavaScript allows us to convert the number to a string for display, the XPath interface will not automatically convert the numerical result if the stringValue property is requested, so the following code will not work:

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var paragraphCount = document.evaluate('count(//p)', document, null, XPathResult.ANY_TYPE, null );
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-alert( 'This document contains ' + paragraphCount.stringValue + ' paragraph elements' );
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Instead it will return an exception with the code NS_DOM_TYPE_ERROR.

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Node-Set-Typen

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The XPathResult object allows node-sets to be returned in 3 principal different types:

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Iteratoren
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When the specified result type in the resultType parameter is either:

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The XPathResult object returned is a node-set of matched nodes which will behave as an iterator, allowing us to access the individual nodes contained by using the iterateNext() method of the XPathResult.

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Once we have iterated over all of the individual matched nodes, iterateNext() will return null.

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Note however, that if the document is mutated (the document tree is modified) between iterations that will invalidate the iteration and the invalidIteratorState property of XPathResult is set to true, and a NS_ERROR_DOM_INVALID_STATE_ERR exception is thrown.

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Iterator Example
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var iterator = document.evaluate('//phoneNumber', documentNode, null, XPathResult.UNORDERED_NODE_ITERATOR_TYPE, null );
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-try {
-  var thisNode = iterator.iterateNext();
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-  while (thisNode) {
-    alert( thisNode.textContent );
-    thisNode = iterator.iterateNext();
-  }
-}
-catch (e) {
-  dump( 'Error: Document tree modified during iteration ' + e );
-}
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Momentabbilder (Snapshots)
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When the specified result type in the resultType parameter is either:

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The XPathResult object returned is a static node-set of matched nodes, which allows us to access each node through the snapshotItem(itemNumber) method of the XPathResult object, where itemNumber is the index of the node to be retrieved. The total number of nodes contained can be accessed through the snapshotLength property.

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Snapshots do not change with document mutations, so unlike the iterators the snapshot does not become invalid, but it may not correspond to the current document, for example the nodes may have been moved, it might contain nodes that no longer exist, or new nodes could have been added.

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Snapshot Example
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var nodesSnapshot = document.evaluate('//phoneNumber', documentNode, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null );
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-for ( var i=0 ; i < nodesSnapshot.snapshotLength; i++ )
-{
-  dump( nodesSnapshot.snapshotItem(i).textContent );
-}
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Erster Knoten
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When the specified result type in the resultType parameter is either:

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The XPathResult object returned is only the first found node that matched the XPath expression. This can be accessed through the singleNodeValue property of the XPathResult object. This will be null if the node set is empty.

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Note that, for the unordered subtype the single node returned might not be the first in document order, but for the ordered subtype you are guaranteed to get the first matched node in the document order.

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First Node Example
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var firstPhoneNumber = document.evaluate('//phoneNumber', documentNode, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null );
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-dump( 'The first phone number found is ' + firstPhoneNumber.singleNodeValue.textContent );
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Die Konstante ANY_TYPE

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When the result type in the resultType parameter is specified as ANY_TYPE, the XPathResult object returned, will be whatever type that naturally results from the evaluation of the expression.

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It could be any of the simple types (NUMBER_TYPE, STRING_TYPE, BOOLEAN_TYPE), but, if the returned result type is a node-set then it will only be an UNORDERED_NODE_ITERATOR_TYPE.

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To determine that type after evaluation, we use the resultType property of the XPathResult object. The constant values of this property are defined in the appendix. None Yet =====Any_Type Example===== <pre> </pre>

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Beispiele

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Innerhalb eines HTML-Dokuments

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The following code is intended to be placed in any JavaScript fragment within or linked to the HTML document against which the XPath expression is to be evaluated.

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To extract all the <h2> heading elements in an HTML document using XPath, the xpathExpression is simply '//h2'. Where, // is the Recursive Descent Operator that matches elements with the nodeName h2 anywhere in the document tree. The full code for this is: link to introductory xpath doc

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var headings = document.evaluate('//h2', document, null, XPathResult.ANY_TYPE, null );
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Notice that, since HTML does not have namespaces, we have passed null for the namespaceResolver parameter.

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Since we wish to search over the entire document for the headings, we have used the document object itself as the contextNode.

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The result of this expression is an XPathResult object. If we wish to know the type of result returned, we may evaluate the resultType property of the returned object. In this case, that will evaluate to 4, an UNORDERED_NODE_ITERATOR_TYPE. This is the default return type when the result of the XPath expression is a node set. It provides access to a single node at a time and may not return nodes in a particular order. To access the returned nodes, we use the iterateNext() method of the returned object:

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var thisHeading = headings.iterateNext();
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-var alertText = 'Level 2 headings in this document are:\n'
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-while (thisHeading) {
-  alertText += thisHeading.textContent + '\n';
-  thisHeading = headings.iterateNext();
-}
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Once we iterate to a node, we have access to all the standard DOM interfaces on that node. After iterating through all the h2 elements returned from our expression, any further calls to iterateNext() will return null.

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Auswertung an einem XML-Dokument innerhalb einer Erweiterung

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The following uses an XML document located at chrome://yourextension/content/peopleDB.xml as an example.

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<?xml version="1.0"?>
-<people xmlns:xul = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" >
-  <person>
-	<name first="george" last="bush" />
-	<address street="1600 pennsylvania avenue" city="washington" country="usa"/>
-	<phoneNumber>202-456-1111</phoneNumber>
-  </person>
-  <person>
-	<name first="tony" last="blair" />
-	<address street="10 downing street" city="london" country="uk"/>
-	<phoneNumber>020 7925 0918</phoneNumber>
-  </person>
-</people>
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To make the contents of the XML document available within the extension, we create an XMLHttpRequest object to load the document synchronously, the variable xmlDoc will contain the document as an XMLDocument object against which we can use the evaluate method

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JavaScript used in the extensions xul/js documents.

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var req = new XMLHttpRequest();
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-req.open("GET", "chrome://yourextension/content/peopleDB.xml", false);
-req.send(null);
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-var xmlDoc = req.responseXML;
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-var nsResolver = xmlDoc.createNSResolver( xmlDoc.ownerDocument == null ? xmlDoc.documentElement : xmlDoc.ownerDocument.documentElement);
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-var personIterator = xmlDoc.evaluate('//person', xmlDoc, nsResolver, XPathResult.ANY_TYPE, null );
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Anmerkung

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When the XPathResult object is not defined, the constants can be retreived in privileged code using Components.interfaces.nsIDOMXPathResult.ANY_TYPE (CI.nsIDOMXPathResult). Similarly, an XPathEvaluator can be created using:

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Components.classes["@mozilla.org/dom/xpath-evaluator;1"].createInstance(Components.interfaces.nsIDOMXPathEvaluator)
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Anhang

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Einen benutzerdefinierten Namensauflöser implementieren

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This is an example for illustration only. This function will need to take namespace prefixes from the xpathExpression and return the URI that corresponds to that prefix. For example, the expression:

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'//xhtml:td/mathml:math'
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will select all MathML expressions that are the children of (X)HTML table data cell elements.

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In order to associate the 'mathml:' prefix with the namespace URI 'http://www.w3.org/1998/Math/MathML' and 'xhtml:' with the URI 'http://www.w3.org/1999/xhtml' we provide a function:

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function nsResolver(prefix) {
-  var ns = {
-    'xhtml' : 'http://www.w3.org/1999/xhtml',
-    'mathml': 'http://www.w3.org/1998/Math/MathML'
-  };
-  return ns[prefix] || null;
-}
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Our call to document.evaluate would then looks like:

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document.evaluate( '//xhtml:td/mathml:math', document, nsResolver, XPathResult.ANY_TYPE, null );
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Einen Standard-Namensrauf für XML-Dokumente implementieren

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As noted in the Implementing a Default Namespace Resolver previously, the default resolver does not handle the default namespace for XML documents. For example with this document:

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<?xml version="1.0" encoding="UTF-8"?>
-<feed xmlns="http://www.w3.org/2005/Atom">
-    <entry />
-    <entry />
-    <entry />
-</feed>
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doc.evaluate('//entry', doc, nsResolver, XPathResult.ANY_TYPE, null) will return an empty set, where nsResolver is the resolver returned by createNSResolver. Passing a null resolver doesn't work any better, either.

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One possible workaround is to create a custom resolver that returns the correct default namespace (the Atom namespace in this case). Note that you still have to use some namespace prefix in your XPath expression, so that the resolver function will be able to change it to your required namespace. E.g.:

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function resolver() {
-    return 'http://www.w3.org/2005/Atom';
-}
-doc.evaluate('//myns:entry', doc, resolver, XPathResult.ANY_TYPE, null)
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Note that a more complex resolver will be required if the document uses multiple namespaces.

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An approach which might work better (and allow namespaces not to be known ahead of time) is described in the next section.

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Using XPath functions to reference elements with a default namespace

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Another approach to match default elements in a non-null namespace (and one which works well for dynamic XPath expressions where the namespaces might not be known), involves referring to a particular element using a form such as [namespace-uri()='http://www.w3.org/1999/xhtml' and name()='p' and @id='_myid']. This circumvents the problem of an XPath query not being able to detect the default namespace on a regularly labeled element.

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Getting specifically namespaced elements and attributes regardless of prefix

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If one wishes to provide flexibility in namespaces (as they are intended) by not necessarily requiring a particular prefix to be used when finding a namespaced element or attribute, one must use special techniques.

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While one can adapt the approach in the above section to test for namespaced elements regardless of the prefix chosen (using local-name() in combination with namespace-uri() instead of name()), a more challenging situation occurs, however, if one wishes to grab an element with a particular namespaced attribute in a predicate (given the absence of implementation-independent variables in XPath 1.0).

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For example, one might try (incorrectly) to grab an element with a namespaced attribute as follows: var xpathlink = someElements[local-name(@*)="href" and namespace-uri(@*)='http://www.w3.org/1999/xlink'];

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This could inadvertently grab some elements if one of its attributes existed that had a local name of "href", but it was a different attribute which had the targeted (XLink) namespace (instead of @href).

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In order to accurately grab elements with the XLink @href attribute (without also being confined to predefined prefixes in a namespace resolver), one could obtain them as follows:

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var xpathEls = 'someElements[@*[local-name() = "href" and namespace-uri() = "http://www.w3.org/1999/xlink"]]'; // Grabs elements with any single attribute that has both the local name 'href' and the XLink namespace
-var thislevel = xml.evaluate(xpathEls, xml, null, XPathResult.ANY_TYPE, null);
-var thisitemEl = thislevel.iterateNext();
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In XPathResult definierte Konstanten

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Result Type Defined ConstantValueDescription
ANY_TYPE0A result set containing whatever type naturally results from evaluation of the expression. Note that if the result is a node-set then UNORDERED_NODE_ITERATOR_TYPE is always the resulting type.
NUMBER_TYPE1A result containing a single number. This is useful for example, in an XPath expression using the count() function.
STRING_TYPE2A result containing a single string.
BOOLEAN_TYPE3A result containing a single boolean value. This is useful for example, in an XPath expression using the not() function.
UNORDERED_NODE_ITERATOR_TYPE4A result node-set containing all the nodes matching the expression. The nodes may not necessarily be in the same order that they appear in the document.
ORDERED_NODE_ITERATOR_TYPE5A result node-set containing all the nodes matching the expression. The nodes in the result set are in the same order that they appear in the document.
UNORDERED_NODE_SNAPSHOT_TYPE6A result node-set containing snapshots of all the nodes matching the expression. The nodes may not necessarily be in the same order that they appear in the document.
ORDERED_NODE_SNAPSHOT_TYPE7A result node-set containing snapshots of all the nodes matching the expression. The nodes in the result set are in the same order that they appear in the document.
ANY_UNORDERED_NODE_TYPE8A result node-set containing any single node that matches the expression. The node is not necessarily the first node in the document that matches the expression.
FIRST_ORDERED_NODE_TYPE9A result node-set containing the first node in the document that matches the expression.
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Siehe auch

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Original Document Information

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