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Описание

С помощью функции CSS attr() можно извлекать значение атрибута выбранного элемента и использовать это значение в таблице стилей. Функция работает и с псевдо-элементами. В этом случае возвращается значение атрибута элемента, для которого формируется псевдо-элемент.

Функцию attr() можно использовать с любым свойством CSS, но поддержка иных свойств, кроме content, является экспериментальной.

Синтаксис

/* Пример простого использования */
attr(data-count);
attr(title);

/* С типом */
attr(src url);
attr(data-count number);
attr(data-width px);

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

Значения

attribute-name
Название атрибута элемента HTML, на который ссылаемся в 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, the attr() expression will be invalid too. If omitted, it defaults to string. The list of valid values are:
Ключевое слово Тип Комментарий Значение по умолчанию
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 <uri> 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>.

Формальный синтаксис

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

где
<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 | %

Пример

p::before {
  content: attr(data-foo) " ";
}
<p data-foo="hello">world</p>

Результат

Спецификации

Specification Status Comment
CSS Values and Units Module Level 3
Определение 'attr()' в этой спецификации.
Кандидат в рекомендации 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)
Определение 'attr()' в этой спецификации.
Рекомендация Limited to the content property; always return a <string>.

Совместимость с браузерами

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!

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 2.0 1.0 (1.7 или ранее) 8 9.0 3.1
Usage in other properties than content and with non-string values  Нет[2] Нет [1] Нет ? ?
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 2.1 1.0 (1.0) 8 10.0 3.1
Usage in other properties than contentand with non-string values  ? Нет [1] Нет ? ?

[1] See баг 435426.

[2] See Баг Chromium 246571

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