@csstools/selector-specificity

What is @csstools/selector-specificity?

@csstools/selector-specificity is an npm package designed to calculate the specificity of CSS selectors. This can be useful for developers who need to understand or manipulate the specificity of their CSS rules, ensuring that styles are applied as intended.

What are @csstools/selector-specificity's main functionalities?

Calculate Specificity

This feature allows you to calculate the specificity of a given CSS selector. The output is an object with properties 'a', 'b', and 'c' representing the specificity components.

const { calculate } = require('@csstools/selector-specificity');

const specificity = calculate('div.class#id');
console.log(specificity); // Output: { a: 1, b: 1, c: 1 }

Compare Specificity

This feature allows you to compare the specificity of two CSS selectors. The output is a number indicating which selector has higher specificity.

const { compare } = require('@csstools/selector-specificity');

const result = compare('div.class#id', 'div#id');
console.log(result); // Output: 1

Other packages similar to @csstools/selector-specificity

specificity

The 'specificity' package is another tool for calculating CSS selector specificity. It provides similar functionality to @csstools/selector-specificity, allowing developers to parse and compare the specificity of CSS selectors. However, it may have a different API and additional features.

css-specificity-calculator

The 'css-specificity-calculator' package offers functionality to calculate the specificity of CSS selectors. It is similar to @csstools/selector-specificity but may have a different approach to handling specificity calculations and comparisons.

README

Selector Specificity

Usage

Add Selector Specificity to your project:

npm install postcss @csstools/selector-specificity --save-dev

import parser from 'postcss-selector-parser';
import { selectorSpecificity } from '@csstools/selector-specificity';

const selectorAST = parser().astSync('#foo:has(> .foo)');
const specificity = selectorSpecificity(selectorAST);

console.log(specificity.a); // 1
console.log(specificity.b); // 1
console.log(specificity.c); // 0

selectorSpecificity takes a single selector, not a list of selectors (not : a, b, c). To compare or otherwise manipulate lists of selectors you need to call selectorSpecificity on each part.

Comparing

The package exports a utility function to compare two specificities.

import { selectorSpecificity, compare } from '@csstools/selector-specificity';

const s1 = selectorSpecificity(ast1);
const s2 = selectorSpecificity(ast2);
compare(s1, s2); // -1 | 0 | 1

• if s1 < s2 then compare(s1, s2) returns a negative number (< 0)
• if s1 > s2 then compare(s1, s2) returns a positive number (> 0)
• if s1 === s2 then compare(s1, s2) returns zero (=== 0)

Prior Art

• keeganstreet/specificity
• bramus/specificity

For CSSTools we always use postcss-selector-parser and want to calculate specificity from this AST.