Document.getElementsByTagName() - Web APIs 编辑
The getElementsByTagName method of Document interface returns an HTMLCollection of elements with the given tag name. The complete document is searched, including the root node. The returned HTMLCollection is live, meaning that it updates itself automatically to stay in sync with the DOM tree without having to call document.getElementsByTagName() again.
Syntax
var elements = document.getElementsByTagName(name);
- elements is a live
HTMLCollection(but see the note below) of found elements in the order they appear in the tree. - name is a string representing the name of the elements. The special string "*" represents all elements.
HTMLCollection; however, this method returns a NodeList in WebKit browsers. See bug 14869 for details.Example
In the following example, getElementsByTagName() starts from a particular parent element and searches top-down recursively through the DOM from that parent element, building a collection of all descendant elements which match the tag name parameter. This demonstrates both document.getElementsByTagName() and the functionally identical Element.getElementsByTagName(), which starts the search at a specific element within the DOM tree.
Clicking the buttons uses getElementsByTagName() to count the descendant paragraph elements of a particular parent (either the document itself or one of two nested <div> elements).
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>getElementsByTagName example</title>
<script>
function getAllParaElems() {
var allParas = document.getElementsByTagName('p');
var num = allParas.length;
alert('There are ' + num + ' paragraph in this document');
}
function div1ParaElems() {
var div1 = document.getElementById('div1');
var div1Paras = div1.getElementsByTagName('p');
var num = div1Paras.length;
alert('There are ' + num + ' paragraph in #div1');
}
function div2ParaElems() {
var div2 = document.getElementById('div2');
var div2Paras = div2.getElementsByTagName('p');
var num = div2Paras.length;
alert('There are ' + num + ' paragraph in #div2');
}
</script>
</head>
<body style="border: solid green 3px">
<p>Some outer text</p>
<p>Some outer text</p>
<div id="div1" style="border: solid blue 3px">
<p>Some div1 text</p>
<p>Some div1 text</p>
<p>Some div1 text</p>
<div id="div2" style="border: solid red 3px">
<p>Some div2 text</p>
<p>Some div2 text</p>
</div>
</div>
<p>Some outer text</p>
<p>Some outer text</p>
<button onclick="getAllParaElems();">
show all p elements in document</button><br />
<button onclick="div1ParaElems();">
show all p elements in div1 element</button><br />
<button onclick="div2ParaElems();">
show all p elements in div2 element</button>
</body>
</html>
Notes
When called on an HTML document, getElementsByTagName() lower-cases its argument before proceeding. This is undesirable when trying to match camelCase SVG elements in a subtree in an HTML document. document.getElementsByTagNameNS() is useful in that case. See also bug 499656.
document.getElementsByTagName() is similar to Element.getElementsByTagName(), except that its search encompasses the whole document.
Specifications
| Specification | Status | Comment |
|---|---|---|
| DOM The definition of 'document.getElementsByTagName' in that specification. | Living Standard |
Browser compatibility
BCD tables only load in the browser
See also
Element.getElementsByTagName()document.getElementById()to return a reference to an element by itsiddocument.getElementsByName()to return a reference to an element by itsnamedocument.querySelector()for powerful selectors via queries like'div.myclass'
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