attr()
function can be used with any CSS property, but support for properties other than content
is experimental, and support for the type-or-unit parameter is sparse.The attr()
CSS function is used to retrieve the value of an attribute of the selected element and use it in the stylesheet. It can also be used on pseudo-elements, in which case the value of the attribute on the pseudo-element's originating element is returned.
/* Simple usage */ attr(data-count); attr(title); /* With type */ attr(src url); attr(data-count number); attr(data-width px); /* With fallback */ attr(data-count number, 0); attr(src url, ""); attr(data-width px, inherit); attr(data-something, "default");
Syntax
Values
attribute-name
- Is the name of an attribute on the HTML element referenced in the CSS.
<type-or-unit>
- Is a keyword representing either the type of the attribute's value, or its unit, as in HTML some attributes have implicit units. If the use of
<type-or-unit>
as a value for the given attribute is invalid, theattr()
expression will be invalid too. If omitted, it defaults tostring
. The list of valid values are:Keyword Associated type Comment Default value string
<string>
The attribute value is treated as a CSS <string>
. It is NOT reparsed, and in particular the characters are used as-is instead of CSS escapes being turned into different characters.An empty string. color
<color>
The attribute value is parsed as a hash (3- or 6-value hash) or a keyword. It must be a valid CSS <string>
value.
Leading and trailing spaces are stripped.currentcolor
url
<url>
The attribute value is parsed as a string that is used inside a CSS url()
function.
Relative URL are resolved relatively to the original document, not relatively to the style sheet.
Leading and trailing spaces are stripped.The url about:invalid
that points to a non-existent document with a generic error condition.integer
<integer>
The attribute value is parsed as a CSS <integer>
. If it is not valid, that is not an integer or out of the range accepted by the CSS property, the default value is used.
Leading and trailing spaces are stripped.0
, or, if0
is not a valid value for the property, the property's minimum value.number
<number>
The attribute value is parsed as a CSS <number>
. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
Leading and trailing spaces are stripped.0
, or, if0
is not a valid value for the property, the property's minimum value.length
<length>
The attribute value is parsed as a CSS <length>
dimension, that is including the unit (e.g.12.5em
). If it is not valid, that is not a length or out of the range accepted by the CSS property, the default value is used.
If the given unit is a relative length,attr()
computes it to an absolute length.
Leading and trailing spaces are stripped.0
, or, if0
is not a valid value for the property, the property's minimum value.em
,ex
,px
,rem
,vw
,vh
,vmin
,vmax
,mm
,cm
,in
,pt
, orpc
<length>
The attribute value is parsed as a CSS <number>
, that is without the unit (e.g.12.5
), and interpreted as a<length>
with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
If the given unit is a relative length,attr()
computes it to an absolute length.
Leading and trailing spaces are stripped.0
, or, if0
is not a valid value for the property, the property's minimum value.angle
<angle>
The attribute value is parsed as a CSS <angle>
dimension, that is including the unit (e.g.30.5deg
). If it is not valid, that is not an angle or out of the range accepted by the CSS property, the default value is used.
Leading and trailing spaces are stripped.0deg
, or, if0deg
is not a valid value for the property, the property's minimum value.deg
,grad
,rad
<angle>
The attribute value is parsed as a CSS <number>
, that is without the unit (e.g.12.5
), and interpreted as an<angle>
with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
Leading and trailing spaces are stripped.0deg
, or, if0deg
is not a valid value for the property, the property's minimum value.time
<time>
The attribute value is parsed as a CSS <time>
dimension, that is including the unit (e.g.30.5ms
). If it is not valid, that is not a time or out of the range accepted by the CSS property, the default value is used.
Leading and trailing spaces are stripped.0s
, or, if0s
is not a valid value for the property, the property's minimum value.s
,ms
<time>
The attribute value is parsed as a CSS <number>
, that is without the unit (e.g.12.5
), and interpreted as an<time>
with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
Leading and trailing spaces are stripped.0s
, or, if0s
is not a valid value for the property, the property's minimum value.frequency
<frequency>
The attribute value is parsed as a CSS <frequency>
dimension, that is including the unit (e.g.30.5kHz
). If it is not valid, that is not a frequency or out of the range accepted by the CSS property, the default value is used.0Hz
, or, if0Hz
is not a valid value for the property, the property's minimum value.Hz
,kHz
<frequency>
The attribute value is parsed as a CSS <number>
, that is without the unit (e.g.12.5
), and interpreted as a<frequency>
with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
Leading and trailing spaces are stripped.0Hz
, or, if0Hz
is not a valid value for the property, the property's minimum value.%
<percentage>
The attribute value is parsed as a CSS <number>
, that is without the unit (e.g.12.5
), and interpreted as a<percentage>
. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used.
If the given value is used as a length,attr()
computes it to an absolute length.
Leading and trailing spaces are stripped.0%
, or, if0%
is not a valid value for the property, the property's minimum value. <fallback>
- The value to be used if the associated attribute is missing or contains an invalid value. If not set, CSS will use the default value defined for each
<type-or-unit>
.
Formal syntax
attr( <attr-name> <type-or-unit>? [, <attr-fallback> ]? )where
<type-or-unit> = string | color | url | integer | number | length | angle | time | frequency | cap | ch | em | ex | ic | lh | rlh | rem | vb | vi | vw | vh | vmin | vmax | mm | Q | cm | in | pt | pc | px | deg | grad | rad | turn | ms | s | Hz | kHz | %
Examples
content property
HTML
<p data-foo="hello">world</p>
CSS
[data-foo]::before { content: attr(data-foo) " "; }
Result
<color> value
This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
HTML
<div class="background" data-background="lime">background expected to be red if your browser does not support advanced usage of attr()</div>
CSS
.background { height: 100vh; }
.background { background-color: red; } .background[data-background] { background-color: attr(data-background color, red); }
Specifications
Specification | Status | Comment |
---|---|---|
CSS Values and Units Module Level 4 The definition of 'attr()' in that specification. |
Editor's Draft | Changed it to work like var() . Property values involving attr() are valid at parse time, and the validation of the attribute value is deferred to computed value time. |
CSS Values and Units Module Level 3 The definition of 'attr()' in that specification. |
Candidate Recommendation |
Added two optional parameters; |
CSS Level 2 (Revision 1) The definition of 'attr()' in that specification. |
Recommendation | Limited to the content property;always returns a <string> . |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
attr() | Chrome Full support 2 | Edge Full support 12 | Firefox Full support 1 | IE Full support 8 | Opera Full support 9 | Safari Full support 3.1 | WebView Android Full support ≤37 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 3.1 | Samsung Internet Android Full support 1.0 |
<fallback> | Chrome No support No | Edge No support No | Firefox No support No | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android No support No | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No |
<type-or-unit> | Chrome No support No | Edge No support No | Firefox No support No | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android No support No | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No |
Legend
- Full support
- Full support
- No support
- No support
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.