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<html><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Keywords" name="Keywords"content="JavaScript, examples, JavaScript: The Definitive Guide"><title>Example 21-10 from JavaScript: The Definitive Guide, Fifth Edition</title><style>body { font-family: arial, sans-serif}.lefttitle { font: bold x-small arial, sans-serif; margin: 5px; letter-spacing: .15em; text-transform:uppercase;}.leftcaption { font: italic x-small sans-serif; margin-bottom: 20px;}#banner { font-family:sans-serif; color:#333; font-size:x-large; font-weight:normal; padding:15px; padding-top: 3px; border-bottom:4px double #666;}#banner h1 { font-size: x-large; margin: 0px; padding: 0px;}#banner .description { font-size:large; margin-left: 2px;}pre { border: solid black 1px; background-color: #ddd; padding: 10px; margin: 0px;} </style></script></head><body><div id="banner"><h1>davidflanagan.com/javascript5</h1><span class="description">Example 21-10 from<i>JavaScript: The Definitive Guide, Fifth Edition</i></span></div><div style="float: left; 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text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><pre>/** * XML.XPathExpression is a class that encapsulates an XPath query and its * associated namespace prefix-to-URL mapping. Once an XML.XPathExpression * object has been created, it can be evaluated one or more times (in one * or more contexts) using the getNode() or getNodes() methods. * * The first argument to this constructor is the text of the XPath expression. * * If the expression includes any XML namespaces, the second argument must * be a JavaScript object that maps namespace prefixes to the URLs that define * those namespaces. The properties of this object are the prefixes, and * the values of those properties are the URLs. */XML.XPathExpression = function(xpathText, namespaces) { this.xpathText = xpathText; // Save the text of the expression this.namespaces = namespaces; // And the namespace mapping if (document.createExpression) { // If we're in a W3C-compliant browser, use the W3C API // to compile the text of the XPath query this.xpathExpr = document.createExpression(xpathText, // This function is passed a // namespace prefix and returns the URL. function(prefix) { return namespaces[prefix]; }); } else { // Otherwise, we assume for now that we're in IE and convert the // namespaces object into the textual form that IE requires. this.namespaceString = ""; if (namespaces != null) { for(var prefix in namespaces) { // Add a space if there is already something there if (this.namespaceString) this.namespaceString += ' '; // And add the namespace this.namespaceString += 'xmlns:' + prefix + '="' + namespaces[prefix] + '"'; } } }};/** * This is the getNodes() method of XML.XPathExpression. It evaluates the * XPath expression in the specified context. The context argument should * be a Document or Element object. The return value is an array * or array-like object containing the nodes that match the expression. */XML.XPathExpression.prototype.getNodes = function(context) { if (this.xpathExpr) { // If we are in a W3C-compliant browser, we compiled the // expression in the constructor. We now evaluate that compiled // expression in the specified context var result = this.xpathExpr.evaluate(context, // This is the result type we want XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null); // Copy the results we get into an array. var a = new Array(result.snapshotLength); for(var i = 0; i < result.snapshotLength; i++) { a[i] = result.snapshotItem(i); } return a; } else { // If we are not in a W3C-compliant browser, attempt to evaluate // the expression using the IE API. try { // We need the Document object to specify namespaces var doc = context.ownerDocument; // If the context doesn't have ownerDocument, it is the Document if (doc == null) doc = context; // This is IE-specific magic to specify prefix-to-URL mapping doc.setProperty("SelectionLanguage", "XPath"); doc.setProperty("SelectionNamespaces", this.namespaceString); // In IE, the context must be an Element not a Document, // so if context is a document, use documentElement instead if (context == doc) context = doc.documentElement; // Now use the IE method selectNodes() to evaluate the expression return context.selectNodes(this.xpathText); } catch(e) { // If the IE API doesn't work, we just give up throw "XPath not supported by this browser."; } }}/** * This is the getNode() method of XML.XPathExpression. It evaluates the * XPath expression in the specified context and returns a single matching * node (or null if no node matches). If more than one node matches, * this method returns the first one in the document. * The implementation differs from getNodes() only in the return type. */XML.XPathExpression.prototype.getNode = function(context) { if (this.xpathExpr) { var result = this.xpathExpr.evaluate(context, // We just want the first match XPathResult.FIRST_ORDERED_NODE_TYPE, null); return result.singleNodeValue; } else { try { var doc = context.ownerDocument; if (doc == null) doc = context; doc.setProperty("SelectionLanguage", "XPath"); doc.setProperty("SelectionNamespaces", this.namespaceString); if (context == doc) context = doc.documentElement; // In IE call selectSingleNode instead of selectNodes return context.selectSingleNode(this.xpathText); } catch(e) { throw "XPath not supported by this browser."; } }};// A utility to create an XML.XPathExpression and call getNodes() on itXML.getNodes = function(context, xpathExpr, namespaces) { return (new XML.XPathExpression(xpathExpr, namespaces)).getNodes(context);};// A utility to create an XML.XPathExpression and call getNode() on itXML.getNode = function(context, xpathExpr, namespaces) { return (new XML.XPathExpression(xpathExpr, namespaces)).getNode(context);};</pre><div class="lefttitle" style="padding:0px; text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><p><script type="text/javascript">amazon_ad_tag="davidflanagancom"; amazon_ad_width="300"; amazon_ad_height="250"; amazon_ad_logo="hide";</script><script type="text/javascript" src="../../www.assoc-amazon.com/s/ads.js" tppabs="http://www.assoc-amazon.com/s/ads.js"></script></div></body></html>⌨️ 快捷键说明
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