Specificity Calculator

A JavaScript module for calculating the specificity of CSS selectors. The module is used on the Specificity Calculator website.

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 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.

Front-end usage

SPECIFICITY.calculate('ul#nav li.active a');   // [{ specificity: '0,1,1,3' }]

Node.js usage

var specificity = require('specificity');
specificity.calculate('ul#nav li.active a');   // [{ specificity: '0,1,1,3' }]

Passing in multiple selectors

You can use comma separation to pass in multiple selectors:

SPECIFICITY.calculate('ul#nav li.active a, body.ie7 .col_3 h2 ~ h2');   // [{ specificity: '0,1,1,3' }, { specificity: '0,0,2,3' }]

Return values

The specificity.calculate function returns an array containing a result object for each selector input. Each result object has the following properties:

• selector: the input
• specificity: the result e.g. 0,1,0,0
• parts: array with details about each part of the selector that counts towards the specificity

Example

var specificity = require('../'),
    result = specificity.calculate('ul#nav li.active a');

console.log(result);

/* result =
[ {
    selector: 'ul#nav li.active a',
    specificity: '0,1,1,3',
    parts: [
      { selector: 'ul', type: 'c', index: 0, length: 2 },
      { selector: '#nav', type: 'a', index: 2, length: 4 },
      { selector: 'li', type: 'c', index: 5, length: 2 },
      { selector: '.active', type: 'b', index: 8, length: 7 },
      { selector: 'a', type: 'c', index: 13, length: 1 }
    ]
} ]
*/

Testing

To install dependencies, run: npm install

Then to test, run: npm test