conversion OKLCH into RGB and RGB into OKLCH in js, simplified

oklch2rgb.js

const multiplyMatrices = (A, B) => {
    return [
        A[0]*B[0] + A[1]*B[1] + A[2]*B[2],
        A[3]*B[0] + A[4]*B[1] + A[5]*B[2],
        A[6]*B[0] + A[7]*B[1] + A[8]*B[2]
    ];
}

const oklch2oklab = ([l, c, h]) => [
    l,
    isNaN(h) ? 0 : c * Math.cos(h * Math.PI / 180),
    isNaN(h) ? 0 : c * Math.sin(h * Math.PI / 180)
]
const oklab2oklch = ([l, a, b]) => [
    l,
    Math.sqrt(a ** 2 + b ** 2),
    Math.abs(a) < 0.0002 && Math.abs(b) < 0.0002 ? NaN : (((Math.atan2(b, a) * 180) / Math.PI % 360) + 360) % 360
];

const rgb2srgbLinear = rgb => rgb.map(c => 
    Math.abs(c) <= 0.04045 ?
        c / 12.92 : 
        (c < 0 ? -1 : 1) * (((Math.abs(c) + 0.055) / 1.055) ** 2.4)
)
const srgbLinear2rgb = rgb => rgb.map(c =>
    Math.abs(c) > 0.0031308 ?
        (c < 0 ? -1 : 1) * (1.055 * (Math.abs(c) ** (1 / 2.4)) - 0.055) :
        12.92 * c
)

const oklab2xyz = lab => {
    const LMSg = multiplyMatrices([
        1,  0.3963377773761749,  0.2158037573099136,
        1, -0.1055613458156586, -0.0638541728258133,
        1, -0.0894841775298119, -1.2914855480194092,
    ], lab)
    const LMS = LMSg.map(val => val ** 3)
    return multiplyMatrices([
         1.2268798758459243, -0.5578149944602171,  0.2813910456659647,
        -0.0405757452148008,  1.1122868032803170, -0.0717110580655164,
        -0.0763729366746601, -0.4214933324022432,  1.5869240198367816
    ], LMS)
}
const xyz2oklab = xyz => {
    const LMS = multiplyMatrices([
        0.8190224379967030, 0.3619062600528904, -0.1288737815209879,
        0.0329836539323885, 0.9292868615863434,  0.0361446663506424,
        0.0481771893596242, 0.2642395317527308,  0.6335478284694309
    ], xyz);
    const LMSg = LMS.map(val => Math.cbrt(val));
    return multiplyMatrices([
        0.2104542683093140,  0.7936177747023054, -0.0040720430116193,
        1.9779985324311684, -2.4285922420485799,  0.4505937096174110,
        0.0259040424655478,  0.7827717124575296, -0.8086757549230774
    ], LMSg);
}
const xyz2rgbLinear = xyz => {
    return multiplyMatrices([
        3.2409699419045226,  -1.537383177570094,   -0.4986107602930034,
       -0.9692436362808796,   1.8759675015077202,   0.04155505740717559,
        0.05563007969699366, -0.20397695888897652,  1.0569715142428786
    ], xyz)
}
const rgbLinear2xyz = rgb => {
    return multiplyMatrices([
        0.41239079926595934, 0.357584339383878,   0.1804807884018343,
        0.21263900587151027, 0.715168678767756,   0.07219231536073371,
        0.01933081871559182, 0.11919477979462598, 0.9505321522496607
    ], rgb)
}

const oklch2rgb = lch => 
    srgbLinear2rgb(xyz2rgbLinear(oklab2xyz(oklch2oklab(lch))))
const rgb2oklch = rgb =>
    oklab2oklch(xyz2oklab(rgbLinear2xyz(rgb2srgbLinear(rgb))))

// taken from https://github.com/color-js/color.js/blob/main/src/spaces/oklch.js
// be aware, that oklch2rgb might return values out of bounds. I believe you should clamp them?
// also for gray colors, hue would be NaN