colorjs.io/src/contrast.js

Let’s get serious about color

import getColor from "./getColor.js";
// import defaults from "./defaults.js";
import { isString } from "./util.js";
import * as contrastAlgorithms from "./contrast/index.js";

/** @import { ColorTypes } from "./types.js" */

// Type re-exports
/** @typedef {import("./types.js").Algorithms} Algorithms */

/**
 *
 * @param {ColorTypes} background
 * @param {ColorTypes} foreground
 * @param {Algorithms | ({ algorithm: Algorithms } & Record<string, any>)} o
 * Algorithm to use as well as any other options to pass to the contrast function
 * @returns {number}
 * @throws {TypeError} Unknown or unspecified algorithm
 */
export default function contrast (background, foreground, o) {
	if (isString(o)) {
		o = { algorithm: o };
	}

	let { algorithm, ...rest } = o || {};

	if (!algorithm) {
		let algorithms = Object.keys(contrastAlgorithms)
			.map(a => a.replace(/^contrast/, ""))
			.join(", ");
		throw new TypeError(
			`contrast() function needs a contrast algorithm. Please specify one of: ${algorithms}`,
		);
	}

	background = getColor(background);
	foreground = getColor(foreground);

	for (let a in contrastAlgorithms) {
		if ("contrast" + algorithm.toLowerCase() === a.toLowerCase()) {
			return contrastAlgorithms[a](background, foreground, rest);
		}
	}

	throw new TypeError(`Unknown contrast algorithm: ${algorithm}`);
}