Can I have an element with an ID that starts with a number?

Question

Can I have an element that has an id that starts with or is completely numbers?

E.g. something like this:

<div id="12"></div>

Answer 1

Can I have a div with id as number?

Yes, you can.

id values that consist solely of digits are perfectly valid in HTML; anything but a space is okay. And although earlier HTML specs were more restrictive (ref, ref), requiring a small set of chars and starting with a letter, browsers never cared, which is a big part of why the HTML5 specification opens things up.

If you're going to use those ids with CSS selectors (e.g, style them with CSS, or locate them with querySelector, querySelectorAll, or a library like jQuery that uses CSS selectors), be aware that it can be a pain, because you can't use an id starting with a digit in a CSS id selector literally; you have to escape it. (For instance, #12 is an invalid CSS selector; you have to write it #\31\32.) For that reason, it's simpler to start it with a letter if you're going to use it with CSS selectors.

Those links above in a list for clarity:

• HTML5 - The ID Attribute
• HTML4 - The ID Attribute and ID and NAME tokens
• CSS 2.1 rules for IDs

Below is an example using a div with the id "12" and doing things with it three ways:

1. With CSS
2. With JavaScript via document.getElementById
3. With JavaScript via document.querySelector (on browsers that support it)

It works on every browser I've ever thrown at it (see list below the code). Live Example:

(function() {
  "use strict";

  document.getElementById("12").style.border = "2px solid black";
  if (document.querySelector) {
    document.querySelector("#\\31\\32").style.fontStyle = "italic";
    display("The font style is set using JavaScript with <code>document.querySelector</code>:");
    display("document.querySelector(\"#\\\\31\\\\32\").style.fontStyle = \"italic\";", "pre");
  } else {
    display("(This browser doesn't support <code>document.querySelector</code>, so we couldn't try that.)");
  }

  function display(msg, tag) {
    var elm = document.createElement(tag || 'p');
    elm.innerHTML = String(msg);
    document.body.appendChild(elm);
  }
})();

#\31\32 {
  background: #0bf;
}
pre {
  border: 1px solid #aaa;
  background: #eee;
}

<div id="12">This div is: <code>&lt;div id="12">...&lt;/div></code>
</div>
<p>In the above:</p>
<p>The background is set using CSS:</p>
<pre>#\31\32 {
    background: #0bf;
}</pre>
<p>(31 is the character code for 1 in hex; 32 is the character code for 2 in hex. You introduce those hex character sequences with the backslash, <a href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">see the CSS spec</a>.)</p>
<p>The border is set from JavaScript using <code>document.getElementById</code>:</p>
<pre>document.getElementById("12").style.border = "2px solid black";</pre>

I've never seen the above fail in a browser. Here's a subset of the browsers I've seen it work in:

• Chrome 26, 34, 39
• IE6, IE8, IE9, IE10, IE11
• Firefox 3.6, 20, 29
• IE10 (Mobile)
• Safari iOS 3.1.2, iOS 7
• Android 2.3.6, 4.2
• Opera 10.62, 12.15, 20
• Konquerer 4.7.4

But again: If you're going to use CSS selectors with the element, it's probably best to start it with a letter; selectors like #\31\32 are pretty tricky to read.

Answer 2

From the HTML 5 specs...

The id attribute specifies its element's unique identifier (ID). [DOM]

The value must be unique amongst all the IDs in the element's home subtree and must contain at least one character. The value must not contain any space characters.

There are no other restrictions on what form an ID can take; in particular, IDs can consist of just digits, start with a digit, start with an underscore, consist of just punctuation, etc.

An element's unique identifier can be used for a variety of purposes, most notably as a way to link to specific parts of a document using fragment identifiers, as a way to target an element when scripting, and as a way to style a specific element from CSS.

Identifiers are opaque strings. Particular meanings should not be derived from the value of the id attribute.

So... yes :)

From the HTML 4.01 specs...

ID 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 (".").

So... no :(

Answer 3

From a maintainability standpoint this is a bad idea. ID's should be at least somewhat descriptive of what they represent. Prefix it with something meaningful to be compliant with what others have already answered with. For example:

<div id ="phoneNumber_12" > </div>

Answer 4

You can also select that type of id(though it is definitely not the best practice to create such an id that starts with a number) by doing the following:

document.querySelector('div[id="12"]'); //or 
document.querySelectorAll('div[id="12"]'); //if you have multiple elements with equal ID.

Answer 5

While TJ Crowder's answer is conceptually good, it doesn't work for descendant CSS selectors.

Escaping only the first character followed by space does work however (as at Chrome 49)

Assume the following HTML snippet:

<td id="123456">
 <div class="blah">
  <div class="yadah">play that funky music</div>
 </div>
</td>

The following statement:

document.querySelector("#\\31 23456 .blah .yadah").style.fontStyle = "italic";

correctly displays play that funky music

Answer 6

As pointed out in other responses, the answer is technically:

ID and NAME tokens 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 (".").

However, as a practical matter, you will be somewhat more limited if you want your documents to work with a variety of browsers, CSS editors, and JavaScript frameworks.

As noted in other responses, jQuery has problems with ids that contain periods and colons.

A more subtle problem is that some browsers have been known to mistakenly treat id attribute values as case-sensitive. That means that if you type id="firstName" in your HTML (lower-case 'f') and .FirstName { color: red } in your CSS (upper-case 'F'), a buggy browsers will not set the element's color to red. Because both definitions use valid characters for the id, you will receive no error from a validation tool.

You can avoid these problems by strictly sticking to a naming convention. For example, if you limit yourself entirely to lower-case characters and always separate words with either hyphens or underscores (but not both, pick one and never use the other), then you have an easy-to-remember pattern. You will never wonder "was it firstName or FirstName?" because you will always know that you should type first_name.

Same Question is Already ask

What are valid values for the id attribute in HTML?

Answer 7

No, In experience, it has to start with a letter. You can use numbers if you want after the first character being a letter.

Answer 8

No. It has to start with a letter. See http://www.electrictoolbox.com/valid-characters-html-id-attribute/. You can use numbers after the first character, however, e.g. a1 or theansweris42.