Function to input color and background color that will change lightness of color to make it more seeable if contrast is too low

makeSeeableColor.js

const RED = 0.2126;
const GREEN = 0.7152;
const BLUE = 0.0722;

const GAMMA = 2.4;

function luminance(r, g, b) {
    const a = [r, g, b].map(v => {
        v /= 255;
        return v <= 0.03928
            ? v / 12.92
            : Math.pow((v + 0.055) / 1.055, GAMMA);
    });
    return a[0] * RED + a[1] * GREEN + a[2] * BLUE;
}

function contrast(rgb1, rgb2) {
    const lum1 = luminance(...rgb1);
    const lum2 = luminance(...rgb2);
    const brightest = Math.max(lum1, lum2);
    const darkest = Math.min(lum1, lum2);
    return (brightest + 0.05) / (darkest + 0.05);
}
function hex2rgb(hex) {
    if(!hex.startsWith('#')) hex = `#${hex}`;
    const r = parseInt(hex.slice(1, 3), 16)
    const g = parseInt(hex.slice(3, 5), 16)
    const b = parseInt(hex.slice(5, 7), 16)
    return [r, g, b];
}
function rgb2hex(r, g, b) {
    return `#${r.toString(16).padStart(2, '0')}${g.toString(16).padStart(2, '0')}${b.toString(16).padStart(2, '0')}`;
}
function rgbToHsl(r, g, b) {
    r /= 255; g /= 255; b /= 255;
    let max = Math.max(r, g, b);
    let min = Math.min(r, g, b);
    let d = max - min;
    let h;
    if (d === 0) h = 0;
    else if (max === r) h = ((((g - b) / d) % 6)+6)%6;
    else if (max === g) h = (b - r) / d + 2;
    else if (max === b) h = (r - g) / d + 4;
    let l = (min + max) / 2;
    let s = d === 0 ? 0 : d / (1 - Math.abs(2 * l - 1));
    return [h * 60, s, l];
}

function hslToRgb(h, s, l) {
    let c = (1 - Math.abs(2 * l - 1)) * s;
    let hp = h / 60.0;
    let x = c * (1 - Math.abs((hp % 2) - 1));
    let rgb1;
    if (isNaN(h)) rgb1 = [0, 0, 0];
    else if (hp <= 1) rgb1 = [c, x, 0];
    else if (hp <= 2) rgb1 = [x, c, 0];
    else if (hp <= 3) rgb1 = [0, c, x];
    else if (hp <= 4) rgb1 = [0, x, c];
    else if (hp <= 5) rgb1 = [x, 0, c];
    else if (hp <= 6) rgb1 = [c, 0, x];
    let m = l - c * 0.5;
    return [
        Math.round(255 * (rgb1[0] + m)),
        Math.round(255 * (rgb1[1] + m)),
        Math.round(255 * (rgb1[2] + m))
    ];
}
// hex, hex -> hex
function makeSeeableColor(color, bg_color) {
    let bg_rgb = hex2rgb(bg_color);
    let rgb = hex2rgb(color);
    let c = contrast(bg_rgb, rgb);
    let hsl = rgbToHsl(...rgb);
    let bg_hsl = rgbToHsl(...bg_rgb);
    if(c < 4.5) {
        if(bg_hsl[2] > 0.7) {
            if(hsl[2] > 0.7) {
                hsl[2] = 0.4;
                if(hsl[1] >= 0.1) hsl[1] -= 0.1;
            }
        }
        if(bg_hsl[2] < 0.4) {
            if(hsl[2] < 0.45) {
                hsl[2] = 0.6;
                if(hsl[1] >= 0.1) hsl[1] -= 0.1;
            }
        }
    }
    return rgb2hex(...hslToRgb(...hsl));
}