Maps CSS specificity data for creating a specificity graph. Based on experience of using specificity graphs.

Interactive example running in the browser.

Install using npm:

npm install css-specificity-map

Include in your code:

var cssSpecificityMap = require('css-specificity-map');

There is a browserify build available in the src/ directory. When included it will make this module available as cssSpecificityMap on the global object.

The main method is .parse() which takes a CSS string and returns an array of data points.

There is also a second, shortcut, method .noID() which can be used if you aren't using ID selectors in your CSS. This is equivalent to calling .parse() with linear_scale: false and no_id: true.

• Type: String

This is the CSS to parse. If the CSS can't be parsed it will throw an error.

• Type: Boolean
• Default: false

By default the specificity is mapped to a logarithmic scale. Setting this to true will use a linear scale.

• Type: Boolean
• Default: false

If you aren't using IDs in your CSS then this will leave a gap of an order of magnitude in the specificty graph between classes and !important annotations. By setting this to true the parser will produce a graph that doesn't measure IDs.

If you set this to true and the parser finds an ID it will throw an error.

• Type: Integer
• Default: 1000

The pseudo specificity assigned to a rule that contains an !important annotation. If no_id is true then this is reduced by a factor of 10.

The parser produces a sequence of data points with the following keys:

• position (x axis)
• specificity (y axis)
• selector (annotation)

For example, the following CSS:

"*{} body{} .main{} #content{} .hidden{display:none !important;}"

Would produce the following result:

[
  {
    "specificity": -1,
    "selector": "*",
    "position": 1
  },
  {
    "specificity": 0,
    "selector": "body",
    "position": 2
  },
  {
    "specificity": 1,
    "selector": ".main",
    "position": 3
  },
  {
    "specificity": 2,
    "selector": "#content",
    "position": 4
  },
  {
    "specificity": 3.004,
    "selector": ".hidden { !important }",
    "position": 5
  }
]

Specificity is calculated as a decimal which will lead to 11 classes having higher specificity than an ID. Whilst this is technically incorrect it is still suitable for the purposes of this visualisation.

• 2014-11-28: v1.0.0 - First stable release.