What values for checked and selected are false?

html

boolean-attributes

html5-specification

checkbox-behavior

byAlex Kataev·Mar 12, 2025

In HTML, Boolean attributes such as checked and selected are considered true by their mere presence. To make them false, simply omit the attribute altogether.

Unchecked checkbox:

<!-- Lonely checkbox awaiting to be checked -->
<input type="checkbox" name="option">

Unselected option:

<select>
  <option value="option1">Option 1</option>
</select>

The principle is clear: no attribute depicts false, while the attribute's presence implies true. Don't bother about "false" or "0" values.

Empty or invalid values? Still checked!

Even if an empty or invalid value is provided to the checked attribute, the checkbox will be checked. Why? Because HTML sees the checked attribute's existence, not its value.

<!-- I may seem empty, but I am checked -->
<input type="checkbox" checked="">
<!-- Classic checkbox, I have the credentials of being checked -->
<input type="checkbox" checked="checked">
<!-- Some may call me untrue, but in HTML, I am checked! -->
<input type="checkbox" checked="false">
<!-- SHOUTING MY CHECkED STATUS -->
<input type="checkbox" checked="CHECKED">

When pairing attributes according to XHTML, remember to use checked="".

Cross-browser fun facts

Using browser tools like Firebug or IE8's Developer Tools might depict the checked state with a twist, but the underlying behavior remains same—each checkbox marked with checked will be checked. Trust me, browsers know their job!

HTML5's true-false wisdom

The HTML5 specification, like a wise old wizard, dictates that the existence of a boolean attribute on an element is equivalent to true. So, checked and selected merely need to be there to mean true, their absence means false. Isn't it just beautifully simple?

Crash course in Boolean attributes

Checkbox etiquettes

A checkbox in all modern browsers (including such legends as Firefox 3.6, Chrome 10, and Internet Explorer 8) will be checked as long as it's going along with the checked attribute:

<!-- Check for all, yaay! -->
<input type="checkbox" checked="checked">
<input type="checkbox" checked="">
<input type="checkbox" checked="CHECKED">
<input type="checkbox" checked="true">
<input type="checkbox" checked="false">

An option inside a select element feels selected if it gets the selected attribute. It doesn't care about its value:

<!-- A select opera: And the chosen one is...-->
<select>
  <option value="1">Not Selected</option>
  <option value="2" selected>Selected</option>
</select>

HTML5's validity mantra

To be considered valid in HTML5, an attribute must either be an empty string or an ASCII case-insensitive match for the name. But HTML is kind; it treats checkboxes as checked or options as selected even if they have an invalid value.

Pro tips for pro developers

Being aware of these behaviors is the key to writing predictable code. So, here are some quick tips:

Omit the checked or selected attribute for unchecked checkboxes or unselected options.
Trust the consistency across browsers. Don't rely on "false" values—explicitly remove the attribute.
Be cautious with DOM manipulation—tweaking an attribute's value might not alter its state.