XPathExpression.evaluate() - Web APIs 编辑

The evaluate() method of the XPathExpression interface executes an XPath expression on the given node or document and returns an XPathResult.

Syntax

XPathResult node.evaluate(contextNode, type, result);

Parameters

contextNode

A Node representing the context to use for evaluating the expression.

type Optional

Specifies the type of result to be returned by evaluating the expression. This must be one of the XPathResult.Constants.

result Optional

Allows to specify a result object which may be reused and returned by this method. If this is specified as null or the implementation does not reuse the specified result, a new result object will be returned.

Return value

An XPathResult object representing the result of evaluating the XPath expression.

Exceptions

INVALID_EXPRESSION_ERR

If the expression is not legal according to the rules of the XPathEvaluator, an XPathException of type INVALID_EXPRESSION_ERR is raised.

TYPE_ERR

In case result cannot be converted to the specified type, an XPathException of type TYPE_ERR is raised.

NAMESPACE_ERR

If the expression contains namespace prefixes which cannot be resolved by the specified XPathNSResolver, a DOMException of type NAMESPACE_ERROR is raised.

WRONG_DOCUMENT_ERR

If the provided context node is from a document that is not supported by the XPathEvaluator, a DOMException of type WRONG_DOCUMENT_ERR is raised.

NOT_SUPPORTED_ERR

If the provided context node is not a type permitted as an XPath context node or the request type is not permitted by the XPathEvaluator, a DOMException of type NOT_SUPPORTED_ERR is raised.

Example

The following example shows the use of the evaluate() method.

HTML

<div>XPath example</div>
<div>Number of &lt;div&gt;s: <output></output></div>

JavaScript

var xpath = "//div";
var evaluator = new XPathEvaluator();
var expression = evaluator.createExpression("//div");
var result = expression.evaluate(document, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE);
document.querySelector("output").textContent = result.snapshotLength;

Result

Specifications