react-daterange-picker-onedesert/src/utils/lightenDarkenColor.js

A React based date range picker

export default function lightenDarkenColor(col, amt) {
  let usePound = false;
  let num;
  let r;
  let b;
  let g;

  if (col[0] === "#") {
    col = col.slice(1);
    usePound = true;
  }

  num = parseInt(col, 16);

  r = (num >> 16) + amt;

  if (r > 255) {
    r = 255;
  } else if (r < 0) {
    r = 0;
  }

  b = ((num >> 8) & 0x00FF) + amt;

  if (b > 255) {
    b = 255;
  } else if (b < 0) {
    b = 0;
  }

  g = (num & 0x0000FF) + amt;

  if (g > 255) {
    g = 255;
  } else if (g < 0) {
    g = 0;
  }

  return (usePound ? "#" : "") + (g | (b << 8) | (r << 16)).toString(16);
}