Fast hex encoding in JS using (roughly) Duff's device

hex.js

const 
  toHexDecoder = new TextDecoder(),
  charCodes = [48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 97, 98, 99, 100, 101, 102], // 0123456789abcdef
  u16Lookup = new Uint16Array(256),
  isLittleEndian = new Uint8Array((new Uint16Array([0x0102]).buffer))[0] === 0x02;

if (isLittleEndian) for (let i = 0; i < 256; i ++) u16Lookup[i] = charCodes[i & 0xF] << 8 | charCodes[(i >>> 4) & 0xF];
else for (let i = 0; i < 256; i ++) u16Lookup[i] = charCodes[i & 0xF] | charCodes[(i >>> 4) & 0xF] << 8;

export function toHex(data) {
  const 
    len = data.length,
    last7 = len - 7,
    out = new Uint16Array(len);
  
  let i = 0;
  while (i < last7) {
    out[i] = u16Lookup[data[i++]];
    out[i] = u16Lookup[data[i++]];
    out[i] = u16Lookup[data[i++]];
    out[i] = u16Lookup[data[i++]]; // 4
    out[i] = u16Lookup[data[i++]];
    out[i] = u16Lookup[data[i++]];
    out[i] = u16Lookup[data[i++]];
    out[i] = u16Lookup[data[i++]]; // 8
  }
  
  while (i < len) {
    out[i] = u16Lookup[data[i++]];
  }

  return toHexDecoder.decode(out);
}