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getElementsByTagNameElement Document encountered in NodeList getElementsByTagName(in DOMString tagname) the first order traversal, no exceptions are thrown, and parameters "*" return all elements under the document or element. Notice here that the returned is a live only containing Element NodeList .Element and Document , added the concept of band namespace ( NodeList getElementsByTagNameNS(in DOMString namespaceURI, in DOMString localName) Element , Document ), introduced localName (only ELEMENT_NODE and ATTRIBUTE_NODE talented).Document , Element ) specifically declares that XML should be sensitive to the case of the label name, while non-XML determines whether it is sensitive according to the style of the document type's own case. In fact, the browser to HTML will first convert the label into lowercase and then go to match, so only the actual tag is named lowercase elements.Document , Element ) will return the type modification in order to HTMLCollection , and explain the localName algorithm produced by HTMLCollection the. Note that the second step of the algorithm actually specifies that the label name is sensitive in non-HTML documents, whereas in an HTML document, any case-size label will be converted to lowercase and then matched, so it can only match to an element with the actual label named lowercase.Dom 1 and Dom 2 HTMLDocument interface define a series of "Dom Tree accessors"
readonly attribute HTMLCollection imagesreadonly attribute HTMLCollection appletsreadonly attribute HTMLCollection linksreadonly attribute HTMLCollection formsreadonly attribute HTMLCollection anchorsattribute HTMLElement bodyThis means that in an HTML document, you can get all the elements, get all the elements with attributes, get all document.images document.links href <a> document.links name The elements with attributes <a> , and document.forms get all <form> the Elements. Additionally the get <body> can be used document.body .
Since HTML5 (W3C,WHATWG) has also been defined document.head , deleted, document.anchors increased acquired <embed> document.embeds and present with the same document.plugins , as well as obtained <script> document.scripts .
Since DOM 1 is Document defined document.documentElement to get the root element and remains so far in the HTML document, the element.
Compatibility
- IE 5.5 does not support
* getting all elements as parameters. More than IE6 IE and the major browsers are implemented according to the standard getElementsByTagName .
- Although
document.scripts , document.embeds and document.plugins until HTML5 is standardized, the current versions of each version of IE and other browsers support
document.headNeed ie9+ to support. Other Dom Tree accessor are basically supported in all versions of IE and in the current browser.
Webkit Code AnalysisSimilar getElementsByName , getElementsByTagName ContainerNode implemented in. Because of the special provisions of XML in the standard, this will be based on the document type, swap TagNodeList or HTMLTagNodeList as NodeListsNodeData::addCacheWithAtomicName<> the template specialization (see WEBCORE/DOM/CONTAINERNODE.CPP).
TagNodeListelementMatchesThis is achieved by:
if (M_localname! = Staratom && m_localname! = Element.localname ( )) return false ; return M_namespaceuri = = Staratom | | M_namespaceuri = = Element.namespaceuri ();
This starAtom is what the standard says * . Whether or not the LocalName matches or is * , and then is better than the NamespaceURI * . Because there is no case conversion step, following the standard is case-sensitive. Note that this is more than the NamespaceURI of the steps relative to getElementsByTagName is redundant, the reason is added because it is getElementsByTagNameNS also used TagNodeList , so you can be lazy to write a more than the NamespaceURI version. But the getElementsByTagNameNS use of the fact is addCacheWithQualifiedName not addCacheWithAtomicName , in fact, addCacheWithQualifiedName and addCacheWithAtomicName the difference is that it takes TagNodeList the direct advance of the template specification only (see webcore/dom/ NODERAREDATA.H)
HTMLTagNodeListelementMatchesThis is achieved by:
if (M_localname = = Staratom ) return true ; Const atomicstring& localname = Element.ishtmlelement ()? m_loweredlocalname:m_localname; return LocalName = = Element.localname ();
According to the standard, if the element being compared is in HTML namespace, it is converted to lowercase and then compared. Note There is no comparison to NamespaceURI, after all it is not getElementsByTagNameNS used (the standard does not specify the getElementsByTagNameNS need to convert the case, so use TagNodeList that case sensitive filter enough).
Follow the standard and WebKit source to explore DOM--get the getElementsByTagName of the element
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