HTML <base> id Attribute

The id attribute on a <base> tag assigns an identifier to the base URL element. The identifier must be unique across the page.

Example

#

An id attribute on a <base> element.

<head>
  <base href="https://en.wikipedia.org/wiki/" id="page-base">
</head>

<nav>
  <a href="Vincent_van_Gogh">Vincent Van Gogh</a> <br />
  <a href="Henri_Matisse">Henri Matisse</a> <br />
  <a href="Paul_Cézanne">Paul Cézanne</a>
</nav>

Using id

The id attribute assigns an identifier to the <base> element.

The identifier must be unique across the page.

The id allows programmatic access to the <base> element.

This gives JavaScript the option to dynamically change the <base> settings.

Tip:  id is a global attribute that can be applied to any HTML element.


Syntax

<base id="identifier" />

Values

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Value Description
identifier A unique alphanumeric string. The id value must begin with a letter ([base-Zbase-z]) and may be followed by any number of letters, digits ([0-9]), hyphens (-), underscores (_), colons (:), and periods (.).

More Examples

A <base> tag with a unique id.
Clicking the button will display the href of this base.

<head>
  <base id="mybase" href="https://en.wikipedia.org/wiki/" >
</head>

<body>
  <nav>
    <a href="Vincent_van_Gogh">Vincent Van Gogh</a> <br />
    <a href="Henri_Matisse">Henri Matisse</a> <br />
    <a href="Paul_Cézanne">Paul Cézanne</a>
  </nav><br/><br/>

  <button onclick="show();">Show base href</button>
</body>

<script>
   let show = () => {
      let element = document.getElementById("mybase");
      alert("Base href = " + element.href);
  }
</script>

Code explanation

The id attribute assigns a unique identifier to the <base> element.

Clicking the button calls JavaScript which locates the <base> using the id.

Once located, the base href value is extracted and displayed.


Browser support

Here is when id support started for each browser:

Chrome
1.0 Sep 2008
Firefox
1.0 Sep 2002
IE/Edge
1.0 Aug 1995
Opera
1.0 Jan 2006
Safari
1.0 Jan 2003

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