RGB colour to single decimal number

rgb-colour-to-number.js

// convert three r,g,b integers (each 0-255) to a single decimal integer (something between 0 and ~16m)
function colourToNumber(r, g, b) {
  return (r << 16) + (g << 8) + (b);
}

// convert it back again (to a string)
function numberToColour(number) {
  const r = (number & 0xff0000) >> 16;
  const g = (number & 0x00ff00) >> 8;
  const b = (number & 0x0000ff);
  
  return [r, g, b];
  // or eg. return `rgb(${r},${g},${b})`;
}

there is a mistake.

  const b = (number & 0xff0000) >> 16;
  const g = (number & 0x00ff00) >> 8;
  const r = (number & 0x0000ff);

where is alpha?

where is alpha?

export function number2color(num) {
num >>>= 0;
const b = num & 0xFF,
g = (num & 0xFF00) >>> 8,
r = (num & 0xFF0000) >>> 16,
a = ((num & 0xFF000000) >>> 24) / 255;
return "rgba(" + [ r, g, b, a ].join(",") + ")";
}