Get relative luminance

get-contrast-ratio calculates the contrast ratio between two CSS color's relative luminances based on this definition from W3C.

It doesn't handle transparency as of yet.

This is the contrast ratio you'll need to care about to pass WCAG requirements.

Installation

$ npm install get-contrast-ratio

Usage

import getContrastRatio from 'get-contrast-ratio';

getContrastRatio('black', 'white'); // 21
getContrastRatio('rgb(0,0,0)', 'rgb(255,255,255)'); // 21
getContrastRatio('black', '#000'); // 1
getContrastRatio('white', '#fff'); // 1
getContrastRatio('hsl(50, 30%, 40%)', 'hsl(50, 30%, 40%)'): // 1

Signature

(color1: string, color2: string } = {}) => number

The string parameters are more specifically strings that can be parsed as colors in CSS.

The return value is a number with two decimals in the range 1 <= number <= 21.