nsIDOMXPathEvaluator 编辑

dom/interfaces/xpath/nsIDOMXPathEvaluator.idlScriptable This interface is used to evaluate XPath expressions against a DOM node. Inherits from: nsISupports Last changed in Gecko 1.7

Implemented by: @mozilla.org/dom/xpath-evaluator;1. To create an instance, use:

var domXPathEvaluator = Components.classes["@mozilla.org/dom/xpath-evaluator;1"]
                        .createInstance(Components.interfaces.nsIDOMXPathEvaluator);

Method overview

nsIDOMXPathExpression createExpression(in DOMString expression, in nsIDOMXPathNSResolver resolver)

nsIDOMXPathNSResolver createNSResolver(in nsIDOMNode nodeResolver);

nsISupports evaluate(in DOMString expression, in nsIDOMNode contextNode, in nsIDOMXPathNSResolver resolver, in unsigned short type, in nsISupports result)

Methods

createExpression()

Creates an nsIDOMXPathExpression which can then be used for (repeated) evaluations.

Note: Prior to Gecko 1.9, you could call this method on documents other than the one you planned to run the XPath against; starting with Gecko 1.9, however, you must call it on the same document.

 nsIDOMXPathExpression createExpression(
   in DOMString expression,
   in nsIDOMXPathNSResolver resolver
 );

Parameters

expression

A string representing the XPath to be created.

resolver

A name space resolver created by createNSResolver(), or a user defined name space resolver. Read more on Implementing a User Defined Namespace Resolver if you wish to take the latter approach.

Return value

An XPath expression, as an nsIDOMXPathExpression object.

createNSResolver()

Creates an nsIDOMXPathExpression which resolves name spaces with respect to the definitions in scope for a specified node. It is used to resolve prefixes within the XPath itself, so that they can be matched with the document. null is common for HTML documents or when no name space prefixes are used.

nsIDOMXPathNSResolver createNSResolver(
  in nsIDOMNode nodeResolver
);

Parameters

nodeResolver

The node to be used as a context for name space resolution.

Return value

A name space resolver.

evaluate()

Evaluate the specified XPath expression.

nsISupports evaluate(
  in DOMString expression,
  in nsIDOMNode contextNode,
  in nsIDOMXPathNSResolver resolver,
  in unsigned short type,
  in nsISupports result
);

Parameters

expression

A string representing the XPath to be evaluated.

contextNode

A DOM Node to evaluate the XPath expression against. To evaluate against a whole document, use the document.documentElement.

resolver

A name space resolver created by createNSResolver(), or a user defined name space resolver. Read more on Implementing a User Defined Namespace Resolver if you wish to take the latter approach.

type

A number that corresponds to one of the type constants of nsIXPathResult.

result

An existing nsIXPathResult to use for the result. Using null will create a new nsIXPathResult.

Return value

An XPath result.

See also

• Introduction to using XPath in JavaScript
• document.evaluate
• DOM Level 3 XPath Specification
• XML Path Language (XPath)REC
• nsIDOMXPathResult
• nsIDOMXPathException