Method to lighten / darken hex colors using Javascript.

color.lighten.ts

export function lighten(color = '#004488', opacity = 1) {
  // Convert to color channels
  const num = parseInt(color.slice(1), 16)
  let R = num >> 16,
    G = (num >> 8) & 0x00ff,
    B = num & 0x0000ff

  // Interpolate channel
  opacity = Math.min(Math.max(opacity, 0), 1)
  R = Math.round(R + (1 - opacity) * (255 - R))
  G = Math.round(G + (1 - opacity) * (255 - G))
  B = Math.round(B + (1 - opacity) * (255 - B))

  // Encode as hex
  return (
    '#' +
    (
      0x1000000 +
      (R < 255 ? (R < 1 ? 0 : R) : 255) * 0x10000 +
      (G < 255 ? (G < 1 ? 0 : G) : 255) * 0x100 +
      (B < 255 ? (B < 1 ? 0 : B) : 255)
    )
      .toString(16)
      .slice(1)
  )
}