getContrast.js

/*!
 * Get the contrasting color for any hex color
 * (c) 2021 Chris Ferdinandi, MIT License, https://gomakethings.com
 * Derived from work by Brian Suda, https://24ways.org/2010/calculating-color-contrast/
 * @param  {String} A hexcolor value
 * @return {String} The contrasting color (black or white)
 */
function getContrast (hexcolor){

	// If a leading # is provided, remove it
	if (hexcolor.slice(0, 1) === '#') {
		hexcolor = hexcolor.slice(1);
	}

	// If a three-character hexcode, make six-character
	if (hexcolor.length === 3) {
		hexcolor = hexcolor.split('').map(function (hex) {
			return hex + hex;
		}).join('');
	}

	// Convert to RGB value
	let r = parseInt(hexcolor.substr(0,2),16);
	let g = parseInt(hexcolor.substr(2,2),16);
	let b = parseInt(hexcolor.substr(4,2),16);

	// Get YIQ ratio
	let yiq = ((r * 299) + (g * 587) + (b * 114)) / 1000;

	// Check contrast
	return (yiq >= 128) ? 'black' : 'white';

}