Why Can\'t I Use a Hash Symbol (#) in My HTML ID and How Do I Fix It?

Using ID Selectors with Hash Characters in HTML and CSS

In HTML, IDs are used to uniquely identify elements. However, issues arise when using special meta-characters, such as the hash (#) symbol, in ID values. This article explores why the following code fails:

<code class="html"><div id='test#1'>test1</div>
<div id='test#2'>test2</div></code>

<code class="css">#test#1 {
    color: red;
}</code>

<code class="javascript">$('#test#2').css('color', 'blue');</code>

Explanation:

Meta-characters, including #, have special meanings in CSS and jQuery selectors. To overcome this, meta-characters must be escaped using backslashes ().

Solution:

CSS:

<code class="css">#test\#1 {
    color: red;
}</code>

jQuery:

<code class="javascript">$('#test\#2').css('color', 'blue');</code>

Recommendation:

It is generally inadvisable to use # in ID values. The W3C recommends using only letters, digits, hyphens, underscores, colons, and periods in IDs.

Alternative Syntax:

Escaping the hash character is an alternative approach, but it is better practice to avoid using # in IDs altogether. For example, instead of id="test#1", use id="test1".

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