converting between numbers and bytes in javascript

number-bytes.js

function bitLength(number) {
  return Math.floor(Math.log2(number)) + 1;
}

function byteLength(number) {
  return Math.ceil(bitLength(number) / 8);
}

function toBytes(number) {
  if (!Number.isSafeInteger(number)) {
    throw new Error("Number is out of range");
  }

  const size = number === 0 ? 0 : byteLength(number);
  const bytes = new Uint8ClampedArray(size);
  let x = number;
  for (let i = (size - 1); i >= 0; i--) {
    const rightByte = x & 0xff;
    bytes[i] = rightByte;
    x = Math.floor(x / 0x100);
  }

  return bytes.buffer;
}

function fromBytes(buffer) {
  const bytes = new Uint8ClampedArray(buffer);
  const size = bytes.byteLength;
  let x = 0;
  for (let i = 0; i < size; i++) {
    const byte = bytes[i];
    x *= 0x100;
    x += byte;
  }
  return x;
}

[0, 1, 2, 3, 0xf, 0xff, 0x100, Number.MAX_SAFE_INTEGER].forEach(n => {
  const tb = toBytes(n);
  const fb = fromBytes(tb);
  console.log(n, tb, fb);
})