从XPath打印元素的结果超过了元素

Question

我想要做的就是从xpath返回一个字符串，但我在CasperJS中使用getElementsByXPath函数时遇到了问题。

var casper = require('casper').create({ 
verbose: false, 
logLevel: 'debug' 
}); 
casper.userAgent("Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko)  Chrome/28.0.1500.72 Safari/537.36"); 
casper.start(); 
casper.thenOpen('http://www.uky.edu', function(){ 
    content = casper.evaluate(function() { 
     return __utils__.getElementsByXPath('//div[@id=\'container\']/section[@id=\'content\']/aside[@class=\'socialTab clearfix\']/div[@id=\'usual2\']/div[@id=\'tabs1\']/figure[@class=\'youTube\']/h4/a'); 
    }); 
}); 

casper.run(function() { 
    this.echo(JSON.stringify(content)); 
    this.echo('completed').exit(); 
}); 

不停止返回数据。它绝对不会返回我正在寻找的特定字符串，而是它将返回整个网页的数据。

我结束了一个几乎空白的网页，只用一个DIV想这一点，得到了同样的问题 我用// DIV的XPath和收到以下

[{"align":"","attributes":{"length":0},"baseURI":"http://download2012.ad.uky.edu/caspertest.php","childElementCount":0,"childNodes":{"0":null,"length":1},"child 
ren":{"length":0},"classList":{"length":0},"className":"","clientHeight":20,"cli 
entLeft":0,"clientTop":0,"clientWidth":384,"contentEditable":"inherit","dataset" 
:{},"dir":"","draggable":false,"firstChild":null,"firstElementChild":"","hidden" 
:false,"id":"","innerHTML":"Test2","innerText":"Test2","isContentEditable":false 
,"lang":"","lastChild":{"attributes":"","baseURI":"http://download2012.ad.uky.ed 
u/caspertest.php","childNodes":{"length":0},"data":"Test2","firstChild":"","last 
Child":"","length":5,"localName":"","namespaceURI":"","nextSibling":"","nodeName 
":"#text","nodeType":3,"nodeValue":"Test2","ownerDocument":null,"parentElement": 
null,"parentNode":null,"prefix":"","previousSibling":"","textContent":"Test2","w 
holeText":"Test2"},"lastElementChild":"","localName":"div","namespaceURI":"http: 
//www.w3.org/1999/xhtml","nextElementSibling":"","nextSibling":null,"nodeName":" 
DIV","nodeType":1,"nodeValue":"","offsetHeight":20,"offsetLeft":8,"offsetParent" 
:{"aLink":"","attributes":{"length":0},"background":"","baseURI":"http://downloa 
d2012.ad.uky.edu/caspertest.php","bgColor":"","childElementCount":1,"childNodes" 
:{"0":null,"1":null,"2":null,"length":3},"children":{"0":null,"length":1},"class 
List":{"length":0},"className":"","clientHeight":300,"clientLeft":0,"clientTop": 
0,"clientWidth":400,"contentEditable":"inherit","dataset":{},"dir":"","draggable 
":false,"firstChild":{"attributes":"","baseURI":"http://download2012.ad.uky.edu/ 
caspertest.php","childNodes":{"length":0},"data":"Test\n","firstChild":"","lastC 
hild":"","length":5,"localName":"","namespaceURI":"","nextSibling":null,"nodeNam 
e": 

等。

Answer 1

您不能从CasperJS的页面上下文中返回DOM元素。如果使用document.querySelectorAll而不是__utils__.getElementsByXPath（带有经过调整的CSS选择器），则结果将是一个undefined值的数组。 __utils__.getElementsByXPath的情况并非如此。返回的DOM元素快照实际上是部分可序列化的。问题在于它们包含对文档的循环引用，并且会不断增长。

从docs：

注：参数和返回值的评估函数必须是一个简单的原始对象。经验法则：如果它可以通过JSON序列化，那么它很好。

闭包，函数，DOM节点等不起作用！

你需要在页面上下文中做所有你想做的事情。例如，元素作为字符串：

content = casper.evaluate(function() { 
    return __utils__.getElementByXPath(someSelector).outerHTML; 
});