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 forms:
- the attribute name alone; e.g.,
attribute
, meaning its implicit value is the empty string - the attribute with a value of the empty string; e.g.,
attribute=""
- the attribute with a value of the attribute's name itself, with no leading or trailing whitespace and case ignored; e.g.,
attribute="attribute"
,attribute="ATTRIBUTE"
Note: The strings "true" and "false" are invalid values. To set the attribute to false
, the attribute should be omitted altogether. 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
:
html
<!-- The following checkboxes will be checked on initial rendering -->
<input type="checkbox" checked />
<input type="checkbox" checked="" />
<input type="checkbox" checked="checked" />
<input type="checkbox" checked="Checked" />
<!-- The following checkbox will not be checked on initial rendering -->
<input type="checkbox" />
See also
- Boolean attributes
- Boolean attributes in HTML specification
- Related glossary terms: