Parses RGB string and returns tuple [R: number, G: number, B: number]

parseRGB.ts

const RGB_VALUES_REGEX = new RegExp(/(rgba?)\((.+)\)/)

function parseRGBStrict(color: string): [number, number, number] | [number, number, number, number] {
  const matches = color.match(RGB_VALUES_REGEX)

  if (!matches) {
    throw new Error("No RGB color string");
  }

  const scheme = matches[1]

  if (scheme !== 'rgb' && scheme !== 'rgba') {
    throw new Error("Not RGB or RGBA color definition");
  }

  const [r, g, b, a, ...rest] = matches[2].split(',')
    .map(v => v.trim())
    .map((rgb, index) => index < 3 && rgb.indexOf('.') < 0 ? parseInt(rgb) : parseFloat(rgb))

  if (typeof a === 'number' && scheme !== 'rgba') {
    throw new Error("RGB string expects 3 values");
  }

  if (typeof a !== 'number' && scheme === 'rgba') {
    throw new Error("RGBA string expects 4 values");
  }

  if (rest.length !== 0) {
    throw new Error("Unexpected number of RGB/RGBA channels");
  }

  return typeof a === 'number' ? [r, g, b, a] : [r, g, b]
}

function parseRGB(color: string): [number, number, number] | [number, number, number, number] | null {
  try { parseRGBStrict(color) } catch (error) {}

  return null
}