index.js

module.exports = shadesOf;

/**
 * Generate Tailwind-compatible shades from a single color
 * @param {string} hex The hex code to generate shades from
 * @param {boolean} halfShades Generate additional shades, e.g. at 150
 * @returns {{[key: number]: string}}
 */
function shadesOf(hex, halfShades = false) {
    const baseColor = hexToRgbArray(hex);
    const black = [0, 0, 0];
    const white = [255, 255, 255];

    let shades = [50, 100, 200, 300, 400, 500, 600, 700, 800, 900];
    if(halfShades) shades = [...shades, 150, 250, 350, 450, 550, 650, 750, 850].sort();

    let result = {};

    for(let shade of shades) {
        const originalShade = shade;

        if(shade === 500) {
            result[shade] = hex;
            continue;
        }

        let isDarkShade = shade > 500;
        if(isDarkShade) shade -= 500;

        const percentage = shade / 500;
        const startColor = isDarkShade ? black : baseColor;
        const endColor = isDarkShade ? baseColor : white;

        result[originalShade] = getColor(percentage, startColor, endColor);
    }

    return result;
}

function hexToRgbArray(hex) {
    const originalHex =  hex;

    hex = hex.replace('#', '');
    if(hex.length === 3) hex = hex + hex;

    const r = hex.substring(0, 2);
    const g = hex.substring(2, 4);
    const b = hex.substring(4, 6);

    const rgb = [r, g, b].map(channel => {
        try {
            channel =  parseInt(channel, 16);
            if(channel < 0 || channel > 255) throw new Error;
            return channel;
        } catch {
            throw new Error(`Invalid hex color provided: ${originalHex}`);
        }
    });

    return rgb;
}

function getColor(percentage, start, end) {
    const rgb = end.map((channel, index) => {
        return Math.round(channel + percentage * (start[index] - channel));
    });

    const hex = '#' + rgb.map(channel => {
        const component = channel.toString(16);
        if(component.length === 1) return '0' + component;
        return component;
    }).join('');
    return hex;
}