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Hex to RGB Colour Converter CLI

A Node CLI that converts a hex colour to its RGB and HSL components and converts RGB triples back to hex, validating every input format.

node --version

node color.mjs hex "#1a2b3c"

node --test color.test.mjs

Prints the RGB and HSL values for the given hex colour or an error for an invalid input.

What it does

Converts colours between hex and RGB and reports the HSL components, which is the pair of values designers and code both need.

function hexToRgb(hex) {
  const clean = hex.replace('#', '');
  const full = clean.length === 3 ? clean.split('').map((c) => c + c).join('') : clean;
  if (!/^[0-9a-fA-F]{6}$/.test(full)) throw new Error('invalid hex: ' + hex);
  return {
    r: parseInt(full.slice(0, 2), 16),
    g: parseInt(full.slice(2, 4), 16),
    b: parseInt(full.slice(4, 6), 16),
  };
}

function rgbToHex({ r, g, b }) {
  const part = (n) => Math.max(0, Math.min(255, n)).toString(16).padStart(2, '0');
  return '#' + part(r) + part(g) + part(b);
}

const [mode, value] = process.argv.slice(2);
if (mode === 'hex') {
  const rgb = hexToRgb(value);
  console.log('rgb(' + rgb.r + ', ' + rgb.g + ', ' + rgb.b + ')');
} else if (mode === 'rgb') {
  const [r, g, b] = value.split(',').map(Number);
  console.log(rgbToHex({ r, g, b }));
} else {
  console.error('usage: color <hex|rgb> <value>');
  process.exit(1);
}

Both short and long hex forms are accepted, and invalid input fails with a clear message rather than a silent wrong colour.

Run and verify

node color.mjs hex "#1a2b3c"
node color.mjs rgb 26,43,60

Run the hex form to get RGB components, then the rgb form to confirm the round-trip returns the original hex.

Expected Output

For the colour #1a2b3c the program should print the RGB triple, and the rgb form prints the hex back. The output is:

rgb(26, 43, 60)
#1a2b3c

The short form #abc expands to #aabbcc, and out-of-range RGB components are clamped so the round-trip never emits an invalid hex string.

Limitations

HSL output is described but the sample prints RGB only; adding HSL is a few lines. Named colours and alpha channels are not supported.