HTML <sub> id Attribute

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

Example

#

An id attribute on a <sub> tag.

The formula for water is H2O.

<p>
  The formula for water is H<sub id="subtwo">2</sub>O.
</p>

Using id

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

The identifier must be unique across the page.

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

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


Syntax

<sub id="identifier" />

Values

#

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

More Examples

A <sub> element with a unique id attribute.
Clicking the button displays the subscript content.

The formula for water is H2O


<p>The formula for water is H<sub id="mysub">2</sub>O</p>
  
<br />
<button onclick="show();">Show sub content</button>

<script>
  let show = () => {
     let element = document.getElementById("mysub");
     alert("Content = " + element.innerHTML);
  }
</script>

Code explanation

The id attribute assigns a unique identifier for the <sub>.

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

Finally, the content of the <sub> is displayed in an alert box.


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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