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WCAG Color

npm (scoped)

According to the WHO an estimated 1.3 billion people live with some form of visual impairment. This includes people who are legally blind and people with less than 20/20 vision.

This library helps you achieve the accessibility standards for color contrast outlined in the WCAG 2.0 specification.

Installation

npm install @opendevtools/wcag-color

API

Ratio

ratio takes two colors, a foreground color, and background color, and returns a contrast ratio. ratio accepts most color formats:

  • HEX - normal (#0088ff), shorthand (#08f) and without hash (08f)
  • RGB - rgb(255, 255, 255)
  • HSL - hsl(210, 100%, 40%)
ratio(foreground: string, background: string) => number

Example

import { ratio } from '@opendevtools/wcag-color'

ratio('hsl(210, 100%, 40%)', '#ffffff') // 5.57

Score

score takes two colors and returns a score value. Read more below.

score(foreground: string, background: string) => 'Fail' | 'AA Large' | 'AA' | 'AAA'

Example

import { score } from '@opendevtools/wcag-color'

score('hsl(210, 100%, 40%)', '#ffffff') // AA

Score from ratio

scoreFromRatio takes a ratio and returns a score value.

scoreFromRatio(ratio: number) => 'Fail' | 'AA Large' | 'AA' | 'AAA'

Example

import { scoreFromRatio } from '@opendevtools/wcag-color'

scoreFromRatio(7.5) // AAA

Best color out of two

best takes two colors and a background color and returns the color which is best suited, from a contrast perspective, for that background color.

best(firstColor: string, secondColor: string, background: string) => string

Example

import { best } from '@opendevtools/wcag-color'

best('#ffffff', '#000000', '#ffffff') // #000000

Score and ratio

  • Fail - Your text has a contrast ratio of less than 3.0
  • AA Large - Least amount of contrast for font size 18px and larger. The ratio is above 3.0.
  • AA - What you should aim for with text sizes below 18px. The ratio is at least 4.5.
  • AAA - Enhanced contrast with a ratio of at least 7.0. Valuable for texts that will be read for a longer period of time.