generate a UUID (taken from ThreeJS)

generateUUID.ts

const lut: string[] = [];

function getLut(): string[] {
  if (lut.length === 0) {
    for (let i = 0, hex = ''; i < 256; i++) {
      hex = i.toString(16);
      lut.push(hex.length === 1 ? `0${hex}` : hex);
    }
  }
  return lut;
}

// http://stackoverflow.com/questions/105034/how-to-create-a-guid-uuid-in-javascript/21963136#21963136
export function generateUUID(): string {
  const _lut = getLut();
  const d0 = (Math.random() * 0xffffffff) | 0;
  const d1 = (Math.random() * 0xffffffff) | 0;
  const d2 = (Math.random() * 0xffffffff) | 0;
  const d3 = (Math.random() * 0xffffffff) | 0;
  const uuid =
    _lut[d0 & 0xff] +
    _lut[(d0 >> 8) & 0xff] +
    _lut[(d0 >> 16) & 0xff] +
    _lut[(d0 >> 24) & 0xff] +
    '-' +
    _lut[d1 & 0xff] +
    _lut[(d1 >> 8) & 0xff] +
    '-' +
    _lut[((d1 >> 16) & 0x0f) | 0x40] +
    _lut[(d1 >> 24) & 0xff] +
    '-' +
    _lut[(d2 & 0x3f) | 0x80] +
    _lut[(d2 >> 8) & 0xff] +
    '-' +
    _lut[(d2 >> 16) & 0xff] +
    _lut[(d2 >> 24) & 0xff] +
    _lut[d3 & 0xff] +
    _lut[(d3 >> 8) & 0xff] +
    _lut[(d3 >> 16) & 0xff] +
    _lut[(d3 >> 24) & 0xff];

  // .toLowerCase() here flattens concatenated strings to save heap memory space.
  return uuid.toLowerCase();
}