Boolean attribute (HTML)

A boolean attribute in HTML is an attribute that represents true or false values. If an HTML tag contains a boolean attribute - no matter the value of that attribute - the attribute is set to true on that element. If an HTML tag does not contain the attribute, the attribute is set to false.

If the attribute is present, it can have one of the following values:

  • no value at all, e.g. attribute
  • the empty string, e.g. attribute=""
  • attribute's name itself, with no leading or trailing whitespace, e.g. attribute="attribute"

Note: The strings "true" and "false" are invalid values. To set the attribute to false, the attribute should not be present in the element tag. Though modern browsers treat any string value as true, you should not rely on that behavior.

Here's an example of a HTML boolean attribute checked:

<!-- The following checkboxes will be checked on initial rendering -->
<input type="checkbox" checked />
<input type="checkbox" checked="" />
<input type="checkbox" checked="checked" />

<!-- The following checkbox will not be checked on initial rendering -->
<input type="checkbox" />

See also