Should provide method to generate IV

[bishopjun11]

The IV should be random and unique for every run of your encryption method.
so best to provide a method to generate IV.
maybe anther method to generate Key.

[webdevelopland]

Here you go:
256 key and 128 iv

function getRandomKey(): Uint8Array {
  return getRandomBlock(32);
}

function getIV(): Uint8Array {
  return getRandomBlock(16);
}

function getRandomBlock(size: number): Uint8Array {
  const block: number[] = [];
  for (let i = 0; i < size; i++) {
    block.push(Math.floor(Math.random() * 256));
  }
  return new Uint8Array(block);
}

[ben-ekw]

Thanks @webdevelopland! Here's the JS equivalent for those who need it:

function getRandomKey() {
    return getRandomBlock(32);
  }

  function getRandomIV() {
    return getRandomBlock(16);
  }

  function getRandomBlock(size) {
    const block = [];
    for (let i = 0; i < size; i++) {
      block.push(Math.floor(Math.random() * 256));
    }
    return new Uint8Array(block);
  }