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A função attr() do CSS  é utilizada para se obter o valor de um determinado atributo do elemento selecionado e usá-lo na folha de estilo. Também pode ser utilizado em pseudo-elementos, nesse caso o valor do atributo no pseudo-elemento do elemento original é retornado.

/* Uso Simples */
attr(data-count);
attr(title);

/* Com o tipo */
attr(src url);
attr(data-count number);
attr(data-width px);

/* Com fallback */
attr(data-count number, 0);
attr(src url, '');
attr(data-width px, inherit);
attr(data-something, 'default');

Nota: A função attr() pode ser utilizada com qualquer propriedade CSS, mas o suporte para propriedades que não sejam content é experimental.

Sintaxe

Valores

nome-do-atributo
É o nome do atributo HTML do elemento referenciado no CSS.
<tipo-ou-unidade>
É uma palavra-chave representando tanto o tipo quanto o valor do atributo, ou sua unidade, assim como no HTML alguns atributos tem unidades implícitas. Se o uso de <tipo-ou-unidade> como um valor para determinado atributo for inválido, a expressão attr() será inválida também. Se omitida, o padrão será string. A lista de valores válidos é:
Palavra-chave Tipo Associado Comentário Valor Padrão
string <string> O valor do atributo é tratado como um CSS <string>. NÃO será reparado, e em particular os caracteres usados . An empty string.
cor <color> O valor do atributo é analisado como hash (3- ou 6-valores hash) ou a palavra-chave. Precisa ser um valor <string> CSS válido.
Os espaços do lead e trail são retirados.
corAtual
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, if 0 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, if 0 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, if 0 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, or pc <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, if 0 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, if 0deg 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, if 0deg 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, if 0s 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, if 0s 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, if 0Hz 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, if 0Hz 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, if 0% 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. The fallback value must be valid where attr() is used, even if it is not used, and must not contain another attr() expression. If attr() is not the sole component value of a property, its <fallback> value must be of the type defined by <type-or-unit>. If not set, CSS will use the default value defined for each <type-or-unit>.

Sintaxe formal

attr( <attr-name> <type-or-unit>? [, <attr-fallback> ]? )

where
<type-or-unit> = string | integer | color | url | integer | number | length | angle | time | frequency | em | ex | px | rem | vw | vh | vmin | vmax | mm | q | cm | in | pt | pc | deg | grad | rad | ms | s | Hz | kHz | %

Exemplos

HTML

<p data-foo="hello">world</p>

CSS

p::before {
  content: attr(data-foo) " ";
}

Resultado

Especificações

Especificação Status Comentário
CSS Values and Units Module Level 3
The definition of 'attr()' in that specification.
Candidata a Recomendação Added two optional parameters; can be used on all properties; may return other values than <string>. These changes are experimental and may be dropped during the CR phase if browser support is too small.
CSS Level 2 (Revision 1)
The definition of 'attr()' in that specification.
Recomendação Limited to the content property; always return a <string>.

Compatibilidade dos Navegadores

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support2121893.1
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support2.1 ? Yes4103.1 ?

Funcionalidade Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Suporte Básico 2.0 (Yes) 1.0 (1.7 or earlier) 8 9.0 3.1
Uso em outras propriedades que não  content e com valores não-string Não suportado[2] Não suportado Não suportado [1] Não suportado Não suportado ?
Funcionalidade Android Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Suporte básico 2.1 (Yes) 1.0 (1.0) 8 10.0 3.1
Uso em outras propriedades que não  content e com valores não-string ? Não suportado Não suportado [1] Não suportado ? ?

[1] See bug 435426.

[2] See Chromium bug 246571

Etiquetas do documento e colaboradores

 Colaboradores desta página: GPrimola, igorParanhos
 Última atualização por: GPrimola,