Difference between revisions of "XPath"

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(→‎Using XPath in Greasemonkey: fixed broken link)
 
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== Using XPath in Greasemonkey ==
== Using XPath in Greasemonkey ==


The most convenient way to use XPath in Greasemonkey scripts is with a [[XPath_Helper|helper function]]. The insides of that function illustrate the less convenient way. The native method is through the <code>document.evaluate</code> function.
The most convenient way to use XPath in Greasemonkey scripts is with a [[XPath_Helper|helper function]].
The insides of that function illustrate the less convenient way.
The native method is through the <code>document.evaluate</code> function.


== XPathResult resultTypes ==
== XPathResult resultTypes ==
* [[XPathResult#resultType_Constants|resultType Constants]]
* [[XPathResult#resultType_Constants|resultType Constants]]
* [http://developer.mozilla.org/en/Introduction_to_using_XPath_in_JavaScript#XPathResult_Defined_Constants Further reading at Mozilla Developer Center]
* [http://developer.mozilla.org/en/Introduction_to_using_XPath_in_JavaScript#XPathResult_Defined_Constants Further reading at Mozilla Developer Center]
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Note that relative [[XPathExpression|XPathExpressions]], that start from some specific node, do not begin with a <code>/</code>. Start them with a period, e.g. <code>.//a</code>, or an axis, e.g. <code>descendant::a</code>. The default axis is <code>child</code>, so just <code>a</code> works to find an immediate descendant.
Note that relative [[XPathExpression|XPathExpressions]], that start from some specific node, do not begin with a <code>/</code>. Start them with a period, e.g. <code>.//a</code>, or an axis, e.g. <code>descendant::a</code>. The default axis is <code>child</code>, so just <code>a</code> works to find an immediate descendant.
== Extensions ==
You can quickly determine the XPath to an element with the [https://addons.mozilla.org/en-US/firefox/addon/1095 XPath Checker] addon. Just right-click an element and select "XPath". A window will pop up with the expression. You can also experiment with new expressions interactively.
Another extension is [[Useful_Tools_for_Script_Writers#XPather | XPather]], which relies on [[Useful_Tools_for_Script_Writers#DOM_Inspector | DOM Inspector]].
In [[Useful_Tools_for_Script_Writers#FireBug|FireBug]], you can right-click a node in the HTML inspector and select "Copy XPath". A <code>$x</code> function (like the XPath helper function linked above but with no support for specifying a context node) is available in the Firebug console.


== Links ==
== Links ==

Latest revision as of 15:48, 3 November 2017


XPath (XML Path Language) is a language for addressing elements in a XML or HTML document. XPathExpressions describe paths in a tree represention of the document.

XPath is very fast compared to manual DOM traversal (see e.g. getElementsByClassName Speed Comparison).

This page is intended for tips and gotchas related to using XPath in Greasemonkey scripts, not complete documentation. See the links below for that.

Using XPath in Greasemonkey

The most convenient way to use XPath in Greasemonkey scripts is with a helper function. The insides of that function illustrate the less convenient way. The native method is through the document.evaluate function.

XPathResult resultTypes

Relative paths

Note that relative XPathExpressions, that start from some specific node, do not begin with a /. Start them with a period, e.g. .//a, or an axis, e.g. descendant::a. The default axis is child, so just a works to find an immediate descendant.

Links