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108 lines
3.6 KiB
Markdown
108 lines
3.6 KiB
Markdown
# Specificity Calculator
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A JavaScript module for calculating and comparing the [specificity of CSS selectors](http://www.w3.org/TR/css3-selectors/#specificity). The module is used on the [Specificity Calculator](http://specificity.keegan.st/) website.
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Specificity Calculator is built for CSS Selectors Level 3. Specificity Calculator isn’t a CSS validator. If you enter invalid selectors it will return incorrect results. For example, the [negation pseudo-class](http://www.w3.org/TR/css3-selectors/#negation) may only take a simple selector as an argument. Using a psuedo-element or combinator as an argument for `:not()` is invalid CSS3 so Specificity Calculator will return incorrect results.
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## Front-end usage
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```js
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SPECIFICITY.calculate('ul#nav li.active a'); // [{ specificity: '0,1,1,3' }]
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```
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## Node.js usage
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```js
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var specificity = require('specificity');
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specificity.calculate('ul#nav li.active a'); // [{ specificity: '0,1,1,3' }]
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```
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## Passing in multiple selectors
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You can use comma separation to pass in multiple selectors:
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```js
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SPECIFICITY.calculate('ul#nav li.active a, body.ie7 .col_3 h2 ~ h2'); // [{ specificity: '0,1,1,3' }, { specificity: '0,0,2,3' }]
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```
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## Return values
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The `specificity.calculate` function returns an array containing a result object for each selector input. Each result object has the following properties:
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* `selector`: the input
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* `specificity`: the result as a string e.g. `0,1,0,0`
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* `specificityArray`: the result as an array of numbers e.g. `[0, 1, 0, 0]`
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* `parts`: array with details about each part of the selector that counts towards the specificity
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## Example
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```js
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var specificity = require('../'),
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result = specificity.calculate('ul#nav li.active a');
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console.log(result);
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/* result =
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[ {
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selector: 'ul#nav li.active a',
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specificity: '0,1,1,3',
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specificityArray: [0, 1, 1, 3],
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parts: [
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{ selector: 'ul', type: 'c', index: 0, length: 2 },
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{ selector: '#nav', type: 'a', index: 2, length: 4 },
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{ selector: 'li', type: 'c', index: 5, length: 2 },
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{ selector: '.active', type: 'b', index: 8, length: 7 },
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{ selector: 'a', type: 'c', index: 13, length: 1 }
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]
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} ]
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*/
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```
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## Comparing two selectors
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Specificity Calculator also exposes a `compare` function. This function accepts two CSS selectors or specificity arrays, `a` and `b`.
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* It returns `-1` if `a` has a lower specificity than `b`
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* It returns `1` if `a` has a higher specificity than `b`
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* It returns `0` if `a` has the same specificity than `b`
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```js
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SPECIFICITY.compare('div', '.active'); // -1
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SPECIFICITY.compare('#main', 'div'); // 1
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SPECIFICITY.compare('span', 'div'); // 0
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SPECIFICITY.compare('span', [0,0,0,1]); // 0
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SPECIFICITY.compare('#main > div', [0,1,0,1]); // 0
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```
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## Ordering an array of selectors by specificity
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You can pass the `SPECIFICITY.compare` function to `Array.prototype.sort` to sort an array of CSS selectors by specificity.
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```js
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['#main', 'p', '.active'].sort(SPECIFICITY.compare); // ['p', '.active', '#main']
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```
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## Command-line usage
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Run `npm install specificity` to install the module locally, or `npm install -g specificity` for global installation. You may need to elevate permissions by `sudo` for the latter. Run `specificity` without arguments to learn about its usage:
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```bash
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$ specificity
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Usage: specificity <selector>
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Computes specificity of a CSS selector.
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```
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Pass a selector as the first argument to get its specificity computed:
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```bash
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$ specificity "ul#nav li.active a"
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0,1,1,3
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```
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## Testing
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To install dependencies, run: `npm install`
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Then to test, run: `npm test`
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