使用 JavaScript 和 XPath 从 DOM 中选择元素
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Selecting element from DOM with JavaScript and XPath
提问by Eric Herlitz
I'm trying to figure out how to select the textarea in the code below using xpath and JavaScript (which is the only option here).
我试图弄清楚如何使用 xpath 和 JavaScript（这是这里唯一的选项）在下面的代码中选择 textarea。
<body>
<div id="calculator">
<div id="calculatorController">
<form action="#" method="get" onsubmit="return false">
<p>
<textarea disabled="disabled"></textarea>
</p>
</form>
...
I'm trying to do something like this
我正在尝试做这样的事情
var element = document.evaluate( '//body/form/p/textarea' ,document, null, XPathResult.ANY_TYPE, null );
// and write back
element.value = "Hello textarea";
But it fails
但它失败了
Anyone keen to help?
有人热心帮忙吗？
Thanks
谢谢
Update below this
下面更新
============================================================
================================================== ==========
The entire block of code looks like this.
Don't forget the window.onload=function()
整个代码块看起来像这样。不要忘记window.onload=function()
<html>
<head>
<script type='text/javascript'>
//<![CDATA[
window.onload=function(){
var element = document.evaluate( '//body//form/p/textarea' ,document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null ).singleNodeValue;
if (element != null) {
element.value = 'Hello textarea';
}
}
//]]>
</script>
</head>
<body>
<div id="calculator">
<div id="calculatorController">
<form action="#" method="get" onsubmit="return false">
<p>
<textarea disabled="disabled"></textarea>
</p>
</form>
</div>
</div>
</body>
</html>
回答by Martin Honnen
The evaluate method does not return a DOM node as you seem to expect. You would need
评估方法不会像您预期的那样返回 DOM 节点。你需要
var element = document.evaluate( '//body//form/p/textarea' ,document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null ).singleNodeValue;
if (element != null) {
element.value = '...';
}
回答by Yann Milin
@Mark Robinson comment is right, your Xpath expression is wrong, you could use one of those :
@Mark Robinson 评论是对的，您的 Xpath 表达式是错误的，您可以使用其中之一：
//body/div/div/form/p/textarea (Mark's example)
//body//form/p/textarea (any form in body)
Plus, the evaluate function will return a XPathResultobject, not the textarea, so you can't do directly element.value
另外，评估函数将返回一个XPathResult对象，而不是 textarea，所以你不能直接做 element.value
Here is your example fixed:
这是您修复的示例：
<body>
<div id="calculator">
<div id="calculatorController">
<form action="#" method="get" onsubmit="return false">
<p>
<textarea disabled="disabled"></textarea>
</p>
</form>
</div>
</div>
</body>
--
——
var element = document.evaluate( '//body/div/div/form/p/textarea' ,document, null, XPathResult.ANY_TYPE, null );
var textarea = element.iterateNext ();
textarea.value = "Hello textarea";
