Validate css properties and expand shorthand css properties
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README.md

CSS Property Validation and Shorthand Expansion

Validate css properties and expand css shorthand properties

Contents

Why

  • Uses MDN data to generate validators and shorthand property expanders
  • Supports experimental properties and values

Installation

$ npm install css-property-parser

Usage

const {
  isShorthandProperty,
  isValidDeclaration,
  getShorthandComputedProperties,
  expandShorthandProperty,
  getShorthandsForProperty,
} = require('css-property-parser');

// isShorthandProperty
// returns boolean indicating if the given property is a shorthand property
console.log(isShorthandProperty('border')); // => true
console.log(isShorthandProperty('color')); // => false

// isValidDeclaration
// returns boolean indicating if the given property value pair is valid
console.log(isValidDeclaration('border', '1px solid black')); // => true
console.log(isValidDeclaration('color', 'rgba(0, 0, 0, .25)')); // => true
console.log(isValidDeclaration('z-index', 'abc')); // => false
console.log(isValidDeclaration('height', 'red')); // => false

// getShorthandComputedProperties
// returns an array of computed property names for the given shorthand
console.log(getShorthandComputedProperties('background'))
// => [
//      "background-image",
//      "background-position",
//      "background-size",
//      "background-repeat",
//      "background-origin",
//      "background-clip",
//      "background-attachment",
//      "background-color"
//     ]
console.log(getShorthandComputedProperties('color')) 
// => ["color"]
console.log(getShorthandComputedProperties('unknown'))
// => []

// expandShorthandProperty
// returns an obejct mapping longhand property names to their values
console.log(expandShorthandProperty('margin', '0 3px 10rem'))
// => {
//      'margin-top': '0',
//      'margin-right': '3px',
//      'margin-bottom': '10rem',
//      'margin-left': '3px',
//     }

console.log(expandShorthandProperty('background', 'fixed padding-box url(image.png) rgb(255, 255, 0) 10px top / cover repeat-x'))
// => {
//      'background-attachment': 'fixed',
//      'background-clip': 'padding-box',
//      'background-origin': 'padding-box',
//      'background-image': 'url(image.png)',
//      'background-repeat': 'repeat-x',
//      'background-color': 'rgb(255, 255, 0)',
//      'background-position': '10px top',
//      'background-size': 'cover',
//     }

console.log(getShorthandsForProperty('border-left-width'));
// => [ 'border-left-width', 'border-left', 'border-width', 'border' ]

API

isShorthandProperty(property: string): boolean

Checks if a given property is a shorthand property

  • property - the property name
  • returns true if property is a shorthand, false otherwise

Examples

isShorthandProperty('border')
// => true

isShorthandProperty('color')
// => false

[Experimental] isValidDeclaration(property: string, value: string): boolean

Checks if the given property, value pair is valid.

  • property - the property name. For example, 'border' or 'color'.
  • value - the property value. For example, '1px solid black'.
  • returns true if the given value is valid for the property. Else, false.

Examples

isValidDeclaration('color', 'currentColor')
// => true

isValidDeclaration('color', 'rgb(0)')
// => false (rgba expects at least 3 parameters)

isValidDeclaration('z-index', '-1')
// => true

isValidDeclaration('z-index', 'abc')
// => false (z-index expects an integer)

isValidDeclaration('width', '300px')
// => true

isValidDeclaration('width', '300ms')
// => false ('ms' is not a valid length unit)

getShorthandComputedProperties(property: string, [recursivelyResolve=false]): Array

Given a shorthand property, returns an array of the computed properties for that shorthand property. If given a known property that is not a shorthand, simply returns the given property. If given an unknown property, returns an empty array.

  • shorthandProperty - the shorthand property name. For example, "background" or "border".
  • [recursivelyResolve=false] - recursively resolve additional longhand properties if the shorthands expand to additional shorthands. For example, the border property expands to border-width, which expands further to border-left-width, border-right-width, etc.
  • returns an array containing the computed properties for the given shorthand property. Returns an empty array if the given property is not a valid property.
Examples
getShorthandComputedProperties('background');
// -> [
//   "background-image",
//   "background-position",
//   "background-size",
//   "background-repeat",
//   "background-origin",
//   "background-clip",
//   "background-attachment",
//   "background-color"
// ]
getShorthandComputedProperties('color');
// -> ["color"]
getShorthandComputedProperties('border', true); 
// -> [
//       'border-width',
//       'border-style',
//       'border-color',
//       'border-bottom-width',
//       'border-left-width',
//       'border-right-width',
//       'border-top-width',
//       'border-bottom-style',
//       'border-left-style',
//       'border-right-style',
//       'border-top-style',
//       'border-bottom-color',
//       'border-left-color',
//       'border-right-color',
//       'border-top-color'
// ];
 getShorthandComputedProperties('unknownProperty');
// -> []

expandShorthandProperty(property: string, value: string, [recursivelyResolve=false], [includeInitialValues=false]): Object

Given a property and value attempts to expand the value into its longhand equivalents. Returns an object mapping the property longhand names to the longhand values. If the property cannot be expanded (i.e. the property is not a shorthand property) simply returns an object mapping the original property to the original value.

  • propertyName - the property name for the given value
  • propertyValue - the value of the property
  • [recursivelyResolve=false] - recursively resolve additional longhand properties if the shorthands expand to additional shorthands. For example, the border property expands to border-width, which expands further to border-left-width, border-right-width, etc.
  • [includeInitialValues=false] - when expanding the shorthand property, fill in any missing longhand values with their initial value. For example, the property declaration "border: 1px" only explicitly sets the "border-width" longhand property. If this param is true, the returned object will fill in the initial values for "border-style" and "border-color". By default, the returned object will only contain the "border-width".
  • throws {ParseError} - if the propertyValue cannot be parsed.
  • throws {UnknownPropertyError} - if the propertyName is not defined in mdn.
  • throws {UnsupportedPropertyError} - if the propertyName is a shorthand property, but we don't support expanding it yet.

Currently supports the following properties:

  • animation
  • background
  • border
  • border-bottom
  • border-color
  • border-left
  • border-radius
  • border-right
  • border-style
  • border-top
  • border-width
  • column-rule
  • columns
  • flex
  • flex-flow
  • font
  • list-style
  • margin
  • outline
  • padding
  • text-decoration
  • text-emphasis
  • transition
Examples
expandShorthandProperty('margin', '0 3px 10rem')
// => {
//      'margin-top': '0',
//      'margin-right': '3px',
//      'margin-bottom': '10rem',
//      'margin-left': '3px',
//     }
expandShorthandProperty('flex', 'initial')
// => {
//  'flex-grow': 'initial',
//  'flex-shrink': 'initial',
//  'flex-basis': 'initial',
// }
expandShorthandProperty('border-radius', '10px 5px 2em / 20px 25px 30%')
// => {
//   'border-top-left-radius': '10px / 20px',
//   'border-top-right-radius': '5px / 25px',
//   'border-bottom-left-radius': '5px / 25px',
//   'border-bottom-right-radius': '2em / 30%',
// }

getShorthandsForProperty(property: string): Array<string>

This function is the inverse of getShorthandComputedProperties.

It returns all properties that set the given property, including the property itself. If the property is unknown, an empty array is returned.

Examples
console.log(getShorthandsForProperty('border-left-width'));
// => [ 'border-left-width', 'border-left', 'border-width', 'border' ]
console.log(getShorthandsForProperty('float'));
// => [ 'float' ]
console.log(getShorthandsForProperty('unknown'));
// => [ ]

isInitialValue(property, value)

Because of the initial keyword and shorthand expansion, there are many possible values that are equivalently identical with the initial value of a css property. This function returns true for all possible values that have the effect of setting a property to its initial value.

  • property - string. the property to which the value is assigned.
  • value string. the value to check.
Examples
console.log(isInitialValue('padding-left', '0'));
// => true
console.log(isInitialValue('padding-left', '0px'));
// => true
console.log(isInitialValue('padding-left', '1px'));
// => false
console.log(isInitialValue('padding', '0'));
// => true
console.log(isInitialValue('padding', '0 0px 0in'));
// => true
console.log(isInitialValue('padding', '1px'));
// => false

initialValues(property, recursivelyResolve, includeShorthands)

Get the initial values for a property.

Returns the initial value or values a property has by default according the CSS specification. If the property's initial value(s) is/are unknown, the global keyword initial is returned.

  • property - (string) the property name
  • recursivelyResolve - (boolean) when given a shorthand property, causes the result to include long hand values.
  • includeShorthands - (boolean) when resolving recursively, causes the the result to include the specified shorthand property as well as any intermediate shorthands of this property set to the initial value.
Examples
console.log(initialValues('border-width'));
// => { 'border-width': 'medium' }
console.log(initialValues('border-width', true));
// => {
//   'border-bottom-width': 'medium',
//   'border-left-width': 'medium',
//   'border-right-width': 'medium',
//   'border-top-width': 'medium',
//   'border-width': 'medium'
// }

initialValue(property)

Get the initial value for a property. Returns a string that is the initial value has by default according the CSS specification. If the property's initial value is unknown, the global keyword initial is returned.

  • property - the css property name
Examples
console.log(initialValue('border-width'));
=> 'medium'

Developer/Contribution HOWTO

To use a locally-built version of css-values-parser:

$ npm install
$ npm run start
$ npm test

This will generate grammars and javascript code required to parse the css properties.