HTML Guides for value

The value of an <input type="date"> must be a full date written as YYYY-MM-DD, so keywords like today and localized dates like 15/03/2025 are rejected.

HTML has no relative date keywords. A date input's value has to be a valid date string: a four-digit year, a two-digit month and a two-digit day, joined by hyphens, as in 2025-03-15. Months and days need their leading zero (2025-3-5 fails), and the value can't include a time, because 2025-03-15T10:00 belongs to type="datetime-local". The min and max attributes of a date input follow the same format. An empty value is allowed and leaves the field blank.

Browsers discard a value they can't parse, so the field shows up empty instead of showing the date you meant. The date picker displays the date in the user's own locale, but the markup always uses YYYY-MM-DD, whatever language the page is written in.

To prefill today's date, write the actual date into value when the server renders the page. On a static page, leave value out and set it from a script after the page loads.

Invalid example

<label for="start">Start date</label>

<input type="date" id="start" name="start" value="today">

Valid example

<label for="start">Start date</label>

<input type="date" id="start" name="start" value="2025-03-15">

Setting today's date with JavaScript

<label for="end">End date</label>

<input type="date" id="end" name="end">

<script>

const now = new Date();

const month = String(now.getMonth() + 1).padStart(2, "0");

const day = String(now.getDate()).padStart(2, "0");

document.getElementById("end").value = now.getFullYear() + "-" + month + "-" + day;

</script>

An li element's value attribute must hold an integer, so a value that starts with anything other than a digit or a minus sign, such as NaN, is invalid.

Inside an ol, value sets the number shown for that list item. The HTML standard requires a valid integer: an optional - followed by one or more digits, like 3 or -1. The validator reads the value one character at a time. This message means the first character was neither - nor a digit, and it quotes that character. A word like first fails on its first letter, and so does a leading + or space.

NaN is JavaScript's "not a number" value. In the markup, it usually means a script or a rich text editor tried to work out the item's number, for example with parseInt() on text that has no digits, and wrote the failed result into the attribute.

Browsers ignore a value they can't parse and number the item as if the attribute weren't there, counting on from the item before it. Removing the attribute keeps the numbering readers see today. If an item needs a specific number, write that integer in value. To start the whole list at a number other than 1, put start on the ol instead. Fix whatever generates the attribute as well, or the bad value can come back the next time the page is edited.

Invalid example

<ol>

<li value="NaN">Preheat the oven to 180 °C.</li>

<li value="NaN">Mix the flour and the sugar.</li>

<li value="NaN">Bake for 25 minutes.</li>

</ol>

Valid example

<ol>

<li>Preheat the oven to 180 °C.</li>

<li>Mix the flour and the sugar.</li>

<li>Bake for 25 minutes.</li>

</ol>

An <input type="button"> element requires a non-empty value attribute because that attribute provides the button's visible label and its accessible name.

Unlike <input type="submit">, which defaults to a browser-provided label like "Submit", <input type="button"> has no default label. Without a value, the button renders as an empty rectangle with no text, and assistive technologies have nothing to announce to the user. The W3C validator flags this as an error because the HTML specification mandates that <input type="button"> must have a value attribute, and it must not be empty.

If you need a button without visible text (for example, an icon-only button), use a <button> element instead. The <button> element can contain child elements like <img> or <span>, and you can give it an accessible name through aria-label or visually hidden text. The <input> element cannot contain child content, so value is its only mechanism for labeling.

Invalid example

<input type="button" onclick="doSomething()">

Valid examples

Add a non-empty value attribute:

<input type="button" value="Click me" onclick="doSomething()">

Or switch to a <button> element, which is more flexible:

<button type="button" onclick="doSomething()">Click me</button>