XPathExpression: evaluate() method

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

Syntax

js-nolint

evaluate(contextNode)
evaluate(contextNode, type)
evaluate(contextNode, type, result)

Parameters

contextNode
- : A {{domxref("Node")}} representing the context to use for evaluating the expression.
type {{optional_inline}}
- : Specifies the type of result to be returned by evaluating the expression. This must be one of the {{domxref("XPathResult", "XPathResult", "Constants")}}.
result {{optional_inline}}
- : 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 {{domxref("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 {{domxref("XPathEvaluator")}}, a {{domxref("DOMException")}} of type INVALID_EXPRESSION_ERR is raised.

TYPE_ERR

In case result cannot be converted to the specified type, a {{domxref("DOMException")}} of type TYPE_ERR is raised.

NAMESPACE_ERR

If the expression contains namespace prefixes which cannot be resolved by the specified XPathNSResolver, a {{domxref("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 {{domxref("XPathEvaluator")}}, a {{domxref("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 {{domxref("XPathEvaluator")}}, a {{domxref("DOMException")}} of type NOT_SUPPORTED_ERR is raised.

Examples

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

HTML

html

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

JavaScript

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