• a11y: Built for checking how readable colors are together
• Simple: Parsing of hex strings, contrast checks
• WCAG: Support for checking both WCAG 2.0 and WCAG 3.0 contrasts
• APCA: Support for the upcoming APCA contrast algorithm

• Installation
  • Deno
  • Node
• Getting started
  • hex
  • wcag
  • wcagContrastValue
  • wcagIsReadable
  • apcaContrastValue
  • apcaToInterpolatedFont
  • apcaValidateFont
  • Utilities
• Inspiration and resources
• License

Installation

Deno

import { apcaContrastValue, hex, wcagContrastValue } from "https://deno.land/x/a11y_color_contrast/mod.ts";

const wcag = wcagContrastValue(hex("#e1e1e1"), hex("#fff"));
const apca = apcaContrastValue(hex("#e1e1e1"), hex("#fff"));

Node

Install the module with your favorite manager: npm add a11y-color-contrast

import { apcaContrastValue, hex, wcagContrastValue } from "a11y-color-contrast";

const wcag = wcagContrastValue(hex("#e1e1e1"), hex("#fff"));
const apca = apcaContrastValue(hex("#e1e1e1"), hex("#fff"));

Getting started

You can also read the documentation on Deno docs.

hex

hex is a utility function to parse a hex string to a [number, number, number], useful if your colors are not in the RBG format. Supports both short and long hex colors, and will strip out the alpha channel when the hex string contains it. Note, the returned tripled will contain NaN if the string cannot be parsed. Use isValidColor to check if the input can be invalid.

// import { hex } from "a11y-color-contrast";
import { hex } from "https://deno.land/x/a11y_color_contrast/mod.ts";

hex("#fff");
hex("#e1e1e1");

// Also support hex4/hex8
hex("#1234");
hex("#11ff0000");

// And missing #
hex("fff");

wcag

Based on the WCAG 2.2 algorithm to calculate how readable two colors are when used together. The first argument is the foreground color and the second the background. By default, the function defaults to checking whether the colors pass the WCAG AAA standard (7:1 contrast ratio) for normal text.

// import { hex, wcag } from "a11y-color-contrast";
import { hex, wcag } from "https://deno.land/x/a11y_color_contrast/mod.ts";

wcag(hex("#fff"), hex("#e1e1e1"));
// { level: "AAA", size: "normal", score: 1.3076906134240802, pass: false }

wcag(hex("#0f0f0f"), hex("#fff"));
// { level: "AAA", size: "normal", score: 19.168645448127652, pass: true }

wcag(hex("#0f0f0f"), hex("#f4f"), { level: "AA" });
// { level: "AA", size: "normal", score: 6.8668010864317885, pass: true }

wcag(hex("#0f0f0f"), hex("#f4f"), { level: "AA", size: "large" });
// { level: "AA", size: "large", score: 6.8668010864317885, pass: true }

wcagContrastValue

A simpler version of the wcag function, this returns the contrast value between two colors based on the WCAG 2.2 algorithm.

// import { hex, wcagContrastValue } from "a11y-color-contrast";
import { hex, wcagContrastValue } from "https://deno.land/x/a11y_color_contrast/mod.ts";

wcagContrastValue(hex("#fff"), hex("#e1e1e1"));
// 1.3076906134240802

wcagContrastValue(hex("#0f0f0f"), hex("#fff"));
// 19.168645448127652

wcagIsReadable

A simpler version of the wcag function, this checks whether two colors used together are readable based on the WCAG parameters passed.

// import { hex, wcagIsReadable } from "a11y-color-contrast";
import { hex, wcagIsReadable } from "https://deno.land/x/a11y_color_contrast/mod.ts";

wcagIsReadable(hex("#fff"), hex("#e1e1e1"));
// false

wcagIsReadable(hex("#0f0f0f"), hex("#fff"));
// true

wcagIsReadable(hex("#0f0f0f"), hex("#f4f"), { level: "AAA" });
// false

wcagIsReadable(hex("#0f0f0f"), hex("#f4f"), { level: "AA" });
// true

apcaContrastValue

Based on the upcoming WCAG 3.0 standard, this function is based on the APCA algorithm to calculate how readable two colors are when used together. The first argument is the foreground color and the second the background. It is highly recommended reading the linked article and resources to get an overview over the differences between the WCAG and APCA standard.

// import { apcaContrastValue, hex } from "a11y-color-contrast";
import { apcaContrastValue, hex } from "https://deno.land/x/a11y_color_contrast/mod.ts";

apcaContrastValue(hex("#fff"), hex("#e1e1e1"));
// -17.5

apcaContrastValue(hex("#0f0f0f"), hex("#fff"));
// 105.5

apcaContrastValue(hex("#0f0f0f"), hex("#f4f"));
// 51.2

apcaToInterpolatedFont

Based on a Lc between two colors, this will find the appropriate font sizes for it. The returned array will show "placeholder" for when the contrast is too low for text and "prohibited" when the contrast is unusable and otherwise a font size. If no font size can be calculated it will return null.

The returned array contains nine values, corresponding to the font useable at font weight 100 at index 0, and so on until weight 900 at index 8.

// import { apcaToInterpolatedFont, hex } from "a11y-color-contrast";
import { apcaToInterpolatedFont, hex } from "https://deno.land/x/a11y_color_contrast/mod.ts";

apcaToInterpolatedFont(-17.5);
//  100 200 300 400 500 600 700 800 900
// [ "placeholder", ...]

apcaToInterpolatedFont(105.5);
//  100  200 300 400   500 600 700 800 900
// [ 39, 25, 18, 14.5, 14, 13, 12, 16, 18 ]

apcaToInterpolatedFont(51.2);
//  100  200 300 400 500 600   700   800   900
// [ 92, 69, 57, 31, 27, 23.5, 20.5, 20.5, 20.5 ]

apcaValidateFont

Based on a Lc value, this function allows you to check whether a given font and weight combination passes the required minimum contrast based on the APCA contrast table.

The first parameter is the Lc value, the second is either a single font size or an array of them and the third, optional parameter is either a single font weight or an array of them. If the weight parameter is undefined, it will default to all the font weights.

// import { apcaValidateFont, hex } from "a11y-color-contrast";
import { apcaValidateFont, hex } from "https://deno.land/x/a11y_color_contrast/mod.ts";

apcaValidateFont(-17.5, 36, 800);
// { "36": { "800": false } }

apcaValidateFont(105.5, [14, 16, 18], [400, 600, 800]);
// {
//   "14": { "400": true, "600": true, "800": false },
//   "16": { "400": true, "600": true, "800": true },
//   "18": { "400": true, "600": true, "800": true }
// }

apcaValidateFont(51.2, [18, 32]);
// {
//   "18": { "100": false, "200": false, ..., "700": false, "800": false, "900": false },
//   "32": { "100": false, "200": false, ..., "500": true, "600": true, "700": true, "800": true, "900": true }
// }

Utility functions

toHex

Converts an RGB triplet to its hex string representation.

// import { toHex } from "a11y-color-contrast";
import { toHex } from "https://deno.land/x/a11y_color_contrast/mod.ts";

toHex([0, 0, 0]);
// "#000000"

isValidColor

Checks whether a color parsed via hex is valid.

// import { isValidColor } from "a11y-color-contrast";
import { isValidColor } from "https://deno.land/x/a11y_color_contrast/mod.ts";

isValidColor([0, 0, 0]);
// true

isValidColor([NaN, 0, 0]);
// false

colorFromObject

Converts an RGB object into an RGB triplet.

// import { colorFromObject } from "a11y-color-contrast";
import { colorFromObject } from "https://deno.land/x/a11y_color_contrast/mod.ts";

colorFromObject({ r: 0, g: 0, b: 0 });
// [0, 0, 0]

Inspiration and resources

• APCA homepage: https://git.apcacontrast.com/
• APCA calculator: https://www.myndex.com/APCA/
• APCA/WCAG calculator: https://www.myndex.com/BPCA/
• Contrast Calculator: https://contrast.tools/
• Accessible Palette: https://accessiblepalette.com/
• It’s time for a more sophisticated color contrast check for data visualizations: https://blog.datawrapper.de/color-contrast-check-data-vis-wcag-apca/

License

MIT