如何在CasperJS中选择带有名称空间的标签？

问题描述

我正在重构RSS，所以我决定用CasperJS编写一些测试。

I'm refactoring a RSS so I decided to write some tests with CasperJS.

RSS的元素之一是 atom：link（）

One of the elements of the RSS is "atom:link" (")

我尝试了这三个代码，但均无效果

I tried this three codes, but none works

test.assertExists("//atom:link", "atom:link tag exists.");

test.assertExists({
    type: 'xpath',
    path: "//atom:link"
}, "atom:link element exists.");

//even this...
test.assertExists({
    type: 'xpath',
    namespace: "xmlns:atom",
    path: "//atom:link"
}, "atom:link element exists.");

RSS代码是：

<?xml version="1.0" encoding="utf-8" ?>
<rss version="2.0" xml:base="http://example.org/" xmlns:atom="http://www.w3.org/2005/Atom"
     xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:media="http://search.yahoo.com/mrss/"
     xmlns:content="http://purl.org/rss/1.0/modules/content/">
    <channel>
        <title>RSS Title</title>
        <description>RSS description</description>
        <link>http://example.org</link>
        <lastBuildDate>Mon, 10 Nov 2014 11:37:02 +0000</lastBuildDate>
        <language>es-ES</language>
        <atom:link rel="self" href="http://example.org/rss/feed.xml"/>
        <item></item>
        <item></item>
    </channel>
</rss>

我在此页面的演示中看到，foo：singers可以通过以下方式访问：

I saw that in a demo in this page http://www.freeformatter.com/xpath-tester.html, foo:singers is accesible by:

//foo:singers

但是在CasperJS中，这似乎行不通...

But in CasperJS seems that this don't work...

任何人都知道如何使用命名空间选择这种元素吗？

Anyone know how to select this kind of elements with a namespace?

推荐答案

CasperJS用于通过XPath解析元素的函数是：

The function which CasperJS uses to resolve elements by XPath is document.evaluate:

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

当您查看 namespaceResolver 始终为 null 。这意味着CasperJS不能使用带有前缀的XPath。如果尝试使用，则会得到

When you look into the source code the namespaceResolver is always null. That means that CasperJS cannot use XPaths with prefixes. If you try it, you get

您必须创建自己的方法来使用。

You would have to create your own method to retrieve elements with a user defined nsResolver.

casper.myXpathExists = function(selector){
    return this.evaluate(function(selector){
        function nsResolver(prefix) {
            var ns = {
                'atom' : 'http://www.w3.org/2005/Atom'
            };
            return ns[prefix] || null;
        }
        return !!document.evaluate(selector,
                document,
                nsResolver,
                XPathResult.ANY_TYPE,
                null).iterateNext(); // retrieve first element
    }, selector);
};
// and later
test.assertTrue(casper.myXpathExists("//atom:link"), "atom:link tag exists.");

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