Please refer to the errata for this document, which may include some normative corrections.
See also translations.
Copyright © 2006-2013 W3C® (MIT, ERCIM, Keio, Beihang), All Rights Reserved. W3C liability, trademark and document use rules apply.
Selectors, which are widely used in CSS, are patterns that match against
elements in a tree structure [SELECT][CSS21]. The Selectors API
specification defines methods for retrieving Element
nodes from the DOM by matching against a group of
selectors. It is often desirable to perform DOM operations on a specific
set of elements in a document. These methods simplify the process of
acquiring specific elements, especially compared with the more verbose
techniques defined and used in the past.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
The Web Applications (WebApps) Working Group has developed a comprehensive Selectors API test suite and has demonstrated interoperability of the features among implementations. Please see the Working Group's implementation report.
Please send comments about this document to public-webapps@w3.org (public archive) with [selectors-api] in the subject. (Please note that a different list was used until mid 2008, so some old messages are archived there instead).
This document was developed by the Web Applications Working Group. A complete list of changes to this document is available.
This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
This section is non-normative.
This specification provides methods for selecting and testing elements
based on whether or not they match a given selector. With these methods,
it is easier to match a set of Element
nodes based on specific criteria, than having to subsequently filter the
result of calling other methods like getElementsByTagName()
.
This section is non-normative.
Some ECMAScript [ECMA-262-5.1] examples:
This is an example table written in HTML 4.01.
<table id="score"> <thead> <tr> <th>Test <th>Result <tfoot> <tr> <th>Average <td>82% <tbody> <tr> <td>A <td>87% <tr> <td>B <td>78% <tr> <td>C <td>81% </table>
In order to obtain the cells containing the results in the table, which
might be done, for example, to plot the values on a graph, there are at
least two approaches that may be taken. Using only the APIs from DOM
Level 2, it requires a script like the following that iterates through
each tr
within each tbody
in the
table
to find the second cell of each row.
var table = document.getElementById("score"); var groups = table.tBodies; var rows = null; var cells = []; for (var i = 0; i < groups.length; i++) { rows = groups[i].rows; for (var j = 0; j < rows.length; j++) { cells.push(rows[j].cells[1]); } }
Alternatively, using the querySelectorAll()
method, that
script becomes much more concise.
var cells = document.querySelectorAll("#score>tbody>tr>td:nth-of-type(2)");
Note that the script operates on the DOM and works independently from the syntax used to create the document. Thus this script will also work correctly for an equivalent table created from well-formed XHTML instead of HTML, or dynamically created and inserted into a document using DOM APIs.
All diagrams, examples and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.
The key words must, must not, should, may and recommended in the normative parts of this document are to be interpreted as described in RFC 2119 [RFC2119].
The following conformance classes are defined (and considered) by this specification:
The terminology used in this specification is that from Selectors [SELECT].
The following features are defined in the DOM Level 3 Core specification [DOM-LEVEL-3-CORE]:
Document
interface.
DocumentFragment
interface.
Element
interface.
NodeList
interface.
Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent.
The IDL used in this specification uses the syntax defined in Web IDL [DOM-BINDINGS].
The construction "Foo
object", where Foo
is
actually an interface, is sometimes used instead of the more accurate
"object implementing the Foo
interface".
This section is non-normative.
Some implementations might have different levels of support for Selectors. If some implementations lack support for some selectors, then the use of such selectors will result in those implementations failing to return the expected results. Authors are advised to check for the DOM Exceptions thrown by these APIs and provide a fallback for graceful degradation.
This section is non-normative.
Extensions of the APIs defined in this specification are strongly discouraged. Implementors, Working Groups and other interested parties should discuss extensions on a relevant public forum, such as public-webapps@w3.org.
It is expected that implementing this specification introduces no new security risks for users.
If, at any time, the implementation detects a situation which would violate security policies, the implementation may abort and raise a security exception. If any other error condition occurs which is not covered directly by this or any other relevant specification, the implementation may abort and raise an appropriate, language-binding-specific or implementation-specific exception.
History theft is a potential privacy issue because the
:visited
pseudo-class in Selectors [SELECT] allows authors to query
which links have been visited.
This is not a new problem, as it can already be exploited
using existing CSS and DOM APIs, such as getComputedStyle()
[DOM-LEVEL-2-STYLE].
In this example, vlinks will acquire a list of links that the user has visited. The author can then obtain the URIs and potentially exploit this knowledge.
var vlinks = document.querySelectorAll(":visited"); for (var i = 0; i < vlinks.length; i++) { doSomethingEvil(vlinks[i].href); }
As defined in Selectors ([SELECT], section 6.6.1), user agents may treat all links as unvisited links. It is recommended that implementations behave consistently with other uses of Selectors supported by the user agent.
The term first used in the definitions of the
methods defined in this specification means first in document
order. The term document order means a
depth-first pre-order traversal of the DOM tree or subtree in question.
The term context node refers to the node upon
which the method was invoked. The term subtrees
refers to the collection of elements that are descendants of the context node. The term matching Element
node refers
to an Element
node that matches the selector string (selectors) that
was passed to the method, according to the rules for matching elements
defined in Selectors [SELECT].
partial interface Document { Element? querySelector(DOMString selectors); NodeList querySelectorAll(DOMString selectors); }; partial interface DocumentFragment { Element? querySelector(DOMString selectors); NodeList querySelectorAll(DOMString selectors); }; partial interface Element { Element? querySelector(DOMString selectors); NodeList querySelectorAll(DOMString selectors); };
The selectors argument for the querySelector
and querySelectorAll
methods accepts
a selector string.
The querySelector()
methods on the Document
, DocumentFragment
, and Element
interfaces must
return the first matching Element
node within the subtrees of the context
node. If there is no matching Element
, the method must return null
.
The querySelectorAll()
methods on
the Document
, DocumentFragment
, and Element
interfaces must
return a NodeList
containing all of
the matching Element
nodes within the
subtrees of the context
node, in document order. If there are no
matching nodes, the method must return an empty NodeList
.
When either querySelector
or
querySelectorAll
are invoked,
the implementation must follow these steps:
Let parsed selector be the result of running the algorithm to parse a selector with selectors as the input.
The implementation must then run the algorithm to evaluate a selector against element nodes in the specified tree or subtrees using parsed selector as the selector to return the required result for the invoked method.
The NodeList
object returned by the
querySelectorAll()
method must be static,
not live ([DOM-LEVEL-3-CORE],
section 1.1.1). Subsequent changes to the structure of the underlying
document must not be reflected in the NodeList
object. This means that the
object will instead contain a list of matching Element
nodes that were in the document
at the time the list was created.
A selector string is a list of one or more
group of
selectors ([SELECT], section 5) that may be surrounded by whitespace and matches the
dom_selectors_group
production.
dom_selectors_group : S* [ selectors_group ] S* ;
The productions for selectors_group
is defined in Selectors
Level 3 ([SELECT],
section 10.1). These groups of selectors should not use
namespace prefixes that need to be resolved.
Implementers are advised that if null
or
undefined
are passed as the value of the selectors
parameter, they are to be handled as defined in WebIDL [DOM-BINDINGS]. Authors are
advised to avoid passing these values.
Authors are advised that while the use of pseudo-elements in selectors is permitted, they will not match any elements in the document, and thus would not result in any elements being returned. Therefore, authors are advised to avoid the use of pseudo-elements in selectors that are passed to the methods defined in this specification.
The steps to parse a selector are as follows:
Let selectors be the selector string input to this algorithm.
Let result be the group of selectors returned as a result
of parsing the selectors according to the grammar for
dom_selectors_group
defined above.
If result is invalid ([SELECT], section
12), raisea
a SYNTAX_ERR
exception ([DOM-LEVEL-3-CORE],
section 1.4) and abort this algorithm.
The steps to evaluate a selector are as follows:
Let element be the element being evaluated.
Let selector group be the selector input into this algotihm.
If any selector in selector group matches element, return true. Otherwise, return false.
Selectors are evaluated against a given element in the context of the entire DOM tree in which the element is located.
If the user agent also supports some level of CSS, the implementation should support the same set of selectors in both these APIs and CSS.
If the group of selectors include namespace prefixes that need to be resolved, the
implementation must raise
a SYNTAX_ERR
exception ([DOM-LEVEL-3-CORE],
section 1.4).
This specification does not provide support for resolving arbitrary namespace prefixes. However, support for a namespace prefix resolution mechanism may be considered for inclusion in a future version of this specification.
A namespace prefix needs to be resolved if the
namespace component is neither empty (e.g. |div
),
representing the null namespace, or an asterisk (e.g. *|div
),
representing any namespace. Since the asterisk or empty namespace prefix
do not need to be resolved, implementations that support the namespace
syntax in Selectors must support these. [SELECT]
The following examples make use of this sample XHTML document.
<html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Selectors API Example</title> </head> <body> <div id="foo"> <p class="warning">This is a sample warning</p> <p class="error">This is a sample error</p> </div> <div id="bar"> <p>...</p> </div> </body> </html>
The methods accept a group of selectors (comma separated) as the
argument. The following example would select all p
elements
in the document that have a class of either "error
" or
"warning
".
var alerts = document.querySelectorAll("p.warning, p.error");
The querySelector()
methods
also accept a group of selectors and they will return the first element
(if any) that matches any of the selectors in the group.
var x = document.querySelector("#foo, #bar");
x would contain the first element in the document with an ID
of either foo
or bar
, or null
if
there is no such element. In the sample document above, it would select
the div
element with the ID of foo
because it
is first in document order. The order of
the selectors used in the parameter has no effect and would have the same
result if the order were reversed, as in:
var x = document.querySelector("#bar, #foo");
The methods can also be invoked on elements. In the following example, assume the event handler is registered on an element, and thus the method is invoked on the target element of the event.
function handle(evt) { var x = evt.target.querySelector("span"); ... // Do something with x }
Even though the method is invoked on an element, selectors are still
evaluated in the context of the entire document. In the following
example, the method will still match the div
element's child
p
element, even though the body
element is not
a descendant of the div
element itself.
var div = document.getElementById("bar"); var p = div.querySelector("body p");
Given this sample fragment that contains a list as a navigation menu:
<ul class="nav"> <li><a href="/">Home</a></li> <li><a href="/products">Products</a></li> <li><a href="/about">About</a></li> </ul>
The following example selects all the li
elements and
demonstrates how to iterate through the collection in a NodeList
.
var lis = document.querySelectorAll("ul.nav>li"); for (var i = 0; i < lis.length; i++) { process(lis.item(i)); }
In ECMAScript, the language binding also allows NodeList
s to be addressed using the
array notation, so that loop could be rewritten like this:
for (var i = 0; i < lis.length; i++) { process(lis[i]); }
Since the NodeList
objects
returned by these methods are not live, changes to the DOM do not affect
the content of the list. Consider the process()
function
called in the previous examples is defined as follows:
function process(elmt) { elmt.parentNode.removeChild(elmt); }
This would cause each selected element to be removed from the DOM, but
each element will remain in the NodeList
. If the list were a live NodeList
, removing an item from the DOM
would also remove the element from the list and adjust the indexes of
subsequent elements. That would have adverse effects upon the loop
because not all selected elements would be processed.
In documents comprising elements from multiple namespaces, it's
possible that some elements from different namespaces share the same
local name. Since this API does not natively support a namespace
resolution mechanism for selectors, obtaining a list of such elements
from a specific namespace, excluding all others, requires additional
processing to filter the result. The following example illustrates a
document containing video
elements from both the SVG and
XHTML namespaces.
<svg id="svg1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> <video id="svgvideo1" xlink:href="myvideo.ogg" width="320" height="240"/> <foreignObject width="100" height="100"> <video id="htmlvideo1" src="myvideo.ogg" xmlns="http://www.w3.org/1999/xhtml">No video1</video> </foreignObject> </svg>
The following script demonstrates how to first select the
video
elements and then filter out the unwanted elements
based on their namespace.
var elms = document.querySelectorAll("svg video"); var result = new Array(); var svgns = "http://www.w3.org/2000/svg" for(var i = 0; i < elms.length; i++) { if(elms[i].namespaceURI == svgns) { result.push(elms[i]); } }
The editors would like to thank to the following people who have contributed to this specification (ordered on first name):
Adam van den Hoven, Alan Gresley, Alex Russell, Arthur Barstow, Aryeh Gregor, Björn Höhrmann, Boris Zbarsky, Cameron McCormack, Charles McCathieNevile, Chris Wilson, Christophe Jolif, Daniel Glazman, Daniel Schierbeck, Dave Massy, David "liorean" Andersson, David Greenspan, David Håsäther, Dean Jackson, Doug Schepers, Erik Dahlström, Francois Remy, Hallvord R. M. Steen, Henri Sivonen, Ian Hickson, Ivan Enderlin, Jean-Yves Bitterlich, Jim Ley, João Eiras, John Resig, Jon Ferraiolo, Jonas Sicking, Jorgen Horstink, Kang-Hao (Kenny) Lu, Karl Dubost, Kartikaya Gupta, L. David Baron, Maciej Stachowiak, Magnus Kristiansen, Marat Tanalin, Martijn, Masataka Yakura, Mihai Sucan, Mohamed Zergaoui, Nicholas C. Zakas, Nicolas Mendoza, Norbert Lindenberg, Philip Taylor, Robert Sayre, Robin Berjon, Sander, Sergey Ilinsky, Simon Pieters, Steven Pemberton, Stewart Brodie Tab Atkins Jr., Tarquin Wilton-Jones, Travis Leithead, and William J. Edney
Special thanks to John Resig and Øyvind Stenhaug for their significant contributions to the testsuite.
Thanks to all those who have helped to improve this specification by sending suggestions and corrections.