CSS selector priority and efficiency optimization_html/css_WEB-ITnose

CSS selector priority and efficiency optimization

Date: 7th of Aug, 2015

Author: HaoyCn

This article collects information about CSS selection from all over the Internet Summarize the article on the device and summarize one by yourself.

Priority of various selectors

important statement 1,0,0,0

ID selector 0,1,0,0

Class selector 0,0,1,0

Pseudo class selector 0,0,1,0

Attribute selector 0,0,1,0

Tag Selector 0,0,0,1

Pseudo element selector 0,0,0,1

Wildcard selector 0,0,0,0

above Among the selectors, in addition, tested

attribute selector = pseudo-class selector (apply the last one)

:last-child{color:red;}[desc]{color:green;}

pseudo-class selector> adjacent selector

:last-child{color:green;}p ~ p{color:blue;}

Adjacent selector = child selector = descendant selector (last one applied)

p~p{color:red;}body p{color:blue;}body > p{color:green;}

descendant selector> tag selector

p ~ p{color:blue;}p{color:green;}

style The influence of position

is the same as , and the application depends on the order of the

Element The priority of the attribute is higher than the above two styles

!important The priority is higher than the above two styles

Remarks

!important BUG in IE6: In the same group of CSS properties, !important does not work. For example:

#selector{color:blue !important;color:green;}

Selector efficiency

The principle of reading selectors is from right to left. Therefore, the last selector on the right we write is called the key selector and has a decisive impact on efficiency.

The following efficiency rankings are provided by @Steve Souders.

ID selector

Class selector

Tag selector

Adjacent selector

Child selector

Descendant selector

Wildcard selector

Attribute selector

Pseudo-class selector

Higher priority may not necessarily be more efficient

For example: #id .class and div#id p.class

The former is more efficient than the latter, and the latter has a higher priority than the former. We need to balance efficiency with prioritization.

Optimization suggestions

Many suggestions are provided at the following URL:

https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Writing_efficie ...

A brief summary is as follows:

Avoid using wildcards

Do not use tag names or class names to modify IDs Rules: If the rule uses an ID selector as the key selector, do not add a tag name to the rule. Because the ID itself is unique, adding tag names will unnecessarily reduce matching efficiency.

Do not use tag names to modify classes: Compared to tags, classes are more unique.

Try to be as specific as possible: the simplest and crudest cause of inefficiency is using too many rules on tags. Adding classes to elements can be subdivided into classes more quickly and can reduce the time it takes for rules to match tags.

About descendant selectors and sub-selectors: Avoid using descendant selectors. If you must use them, it is recommended to use sub-selectors instead. However, sub-selectors should also be used with caution. Tag rules should never be used. Contains child selectors.

Take advantage of inheritability: there is no need to declare styles on general content.