XPathResult 的评估返回错误答案

【问题标题】：Evaluation of XPathResult is returning an errorXPathResult 的评估返回错误
【发布时间】：2020-07-24 14:00:20
【问题描述】：

我有一个 xml，我想读取它的 <block> 节点。但是当我在 XPath 下面执行时，它给了我一个错误。

我要解析的 xml：

   let x = `<xml>
    <block type="block_onGreenFlagClicked" id=";]jZ*Zs|[L-Sr{nhCB%V" x="25" y="0">
         <field name="NAME1">When</field>
         <statement name="function_name">
            <block type="helper_Player__walkSecondsDrop" id="9lo_/{gKTxB6/FRH2Pw">
             <field name="LABEL">Player.</field>
             <field name="DROP_Player__walkSecondsDrop$">walkForwardForNSeconds</field>
           </block>
       </statement>
    </block>
    </xml>`;



let doms = new DOMParser()
let v = doms.parseFromString(x, 'text/xml')
let r =  v.evaluate('/block',v, null, XPathResult.ANY_TYPE, null)

下面是结果：

XPathResult {invalidIteratorState: false, resultType: 4, iterateNext: function, snapshotItem: function, ANY_TYPE: 0…}
  booleanValue: [Exception: TypeError: Failed to read the 'booleanValue' property from 'XPathResult': The result type is not a boolean.]
  invalidIteratorState: false
  numberValue: [Exception: TypeError: Failed to read the 'numberValue' property from 'XPathResult': The result type is not a number.]
  resultType: 4
  singleNodeValue: [Exception: TypeError: Failed to read the 'singleNodeValue' property from 'XPathResult': The result type is not a single node.]
  snapshotLength: [Exception: TypeError: Failed to read the 'snapshotLength' property from 'XPathResult': The result type is not a snapshot.]
  stringValue: [Exception: TypeError: Failed to read the 'stringValue' property from 'XPathResult': The result type is not a string.]
  __proto__: XPathResult

我不知道我做错了什么？有人可以指导我吗？

【问题讨论】：

您的 xml 中有两个 <block> 节点，一个是另一个的子节点；你的目标是哪一个？你认为r 的值是多少？

标签： javascript xml xpath xml-parsing xmlhttprequest

【解决方案1】：

代码没有问题。 /block XPath 表达式没有选择任何内容，因为根元素是 xml 元素。将表达式更改为 //block 会选择这两个 block 元素。示例：

let x = `<xml>
    <block type="block_onGreenFlagClicked" id=";]jZ*Zs|[L-Sr{nhCB%V" x="25" y="0">
         <field name="NAME1">When</field>
         <statement name="function_name">
            <block type="helper_Player__walkSecondsDrop" id="9lo_/{gKTxB6/FRH2Pw">
             <field name="LABEL">Player.</field>
             <field name="DROP_Player__walkSecondsDrop$">walkForwardForNSeconds</field>
           </block>
       </statement>
    </block>
    </xml>`
let doms = new DOMParser()
let v = doms.parseFromString(x, 'text/xml')
let r = v.evaluate('//block', v, null, XPathResult.ANY_TYPE, null)

var s = new XMLSerializer();
var t = document.getElementById("output");
while ((n = r.iterateNext())) {
  t.value += (s.serializeToString(n)) + "\n";
}

<body>
  <textarea id="output" rows="15" cols="60"></textarea>
</body>

【讨论】：