58 lines
2.1 KiB
Markdown
58 lines
2.1 KiB
Markdown
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# Selector Specificity
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[<img alt="npm version" src="https://img.shields.io/npm/v/@csstools/selector-specificity.svg" height="20">][npm-url]
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[<img alt="Build Status" src="https://github.com/csstools/postcss-plugins/workflows/test/badge.svg" height="20">][cli-url]
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[<img alt="Discord" src="https://shields.io/badge/Discord-5865F2?logo=discord&logoColor=white">][discord]
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## Usage
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Add [Selector Specificity] to your project:
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```bash
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npm install @csstools/selector-specificity --save-dev
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```
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```js
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import parser from 'postcss-selector-parser';
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import { selectorSpecificity } from '@csstools/selector-specificity';
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const selectorAST = parser().astSync('#foo:has(> .foo)');
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const specificity = selectorSpecificity(selectorAST);
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console.log(specificity.a); // 1
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console.log(specificity.b); // 1
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console.log(specificity.c); // 0
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```
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_`selectorSpecificity` takes a single selector, not a list of selectors (not : `a, b, c`).
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To compare or otherwise manipulate lists of selectors you need to call `selectorSpecificity` on each part._
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### Comparing
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The package exports a utility function to compare two specificities.
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```js
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import { selectorSpecificity, compare } from '@csstools/selector-specificity';
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const s1 = selectorSpecificity(ast1);
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const s2 = selectorSpecificity(ast2);
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compare(s1, s2); // -1 | 0 | 1
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```
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- if `s1 < s2` then `compare(s1, s2)` returns a negative number (`< 0`)
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- if `s1 > s2` then `compare(s1, s2)` returns a positive number (`> 0`)
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- if `s1 === s2` then `compare(s1, s2)` returns zero (`=== 0`)
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## Prior Art
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- [keeganstreet/specificity](https://github.com/keeganstreet/specificity)
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- [bramus/specificity](https://github.com/bramus/specificity)
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For CSSTools we always use `postcss-selector-parser` and want to calculate specificity from this AST.
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[cli-url]: https://github.com/csstools/postcss-plugins/actions/workflows/test.yml?query=workflow/test
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[discord]: https://discord.gg/bUadyRwkJS
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[npm-url]: https://www.npmjs.com/package/@csstools/selector-specificity
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[Selector Specificity]: https://github.com/csstools/postcss-plugins/tree/main/packages/selector-specificity
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