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Document: getElementsByTagName() method - Web APIs

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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.

getElementsByTagName(name)

name

A string representing the name of the elements. The special string * represents all elements.

A live HTMLCollection of found elements in the order they appear in the tree.

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).

<p>Some outer text</p>
<p>Some outer text</p>

<div id="div1">
  <p>Some div1 text</p>
  <p>Some div1 text</p>
  <p>Some div1 text</p>

  <div id="div2">
    <p>Some div2 text</p>
    <p>Some div2 text</p>
  </div>
</div>

<p>Some outer text</p>
<p>Some outer text</p>

<button id="btn1">Show all p elements in document</button>
<br />
<button id="btn2">Show all p elements in div1 element</button>
<br />
<button id="btn3">Show all p elements in div2 element</button>

body {
  border: solid green 3px;
}

#div1 {
  border: solid blue 3px;
}

#div2 {
  border: solid red 3px;
}

function getAllParaElems() {
  const allParas = document.getElementsByTagName("p");
  const num = allParas.length;
  alert(`There are ${num} paragraph in this document`);
}

function div1ParaElems() {
  const div1 = document.getElementById("div1");
  const div1Paras = div1.getElementsByTagName("p");
  const num = div1Paras.length;
  alert(`There are ${num} paragraph in #div1`);
}

function div2ParaElems() {
  const div2 = document.getElementById("div2");
  const div2Paras = div2.getElementsByTagName("p");
  const num = div2Paras.length;
  alert(`There are ${num} paragraph in #div2`);
}

document.getElementById("btn1").addEventListener("click", getAllParaElems);
document.getElementById("btn2").addEventListener("click", div1ParaElems);
document.getElementById("btn3").addEventListener("click", div2ParaElems);

When called on an HTML document, getElementsByTagName() lower-cases its argument before proceeding. This is undesirable when trying to match camel case SVG elements in a subtree in an HTML document. document.getElementsByTagNameNS() is useful in that case. See also Firefox bug 499656.

document.getElementsByTagName() is similar to Element.getElementsByTagName(), except that its search encompasses the whole document.

• Element.getElementsByTagName()
• document.getElementById() to return a reference to an element by its id
• document.getElementsByName() to return a reference to an element by its name
• document.querySelector() for powerful selectors via queries like 'div.myclass'

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