Does this have side effects?

read-stream-functional.js

export const readUint16 = (typedArr, offset) => {
  const buf = new ArrayBuffer(2)
  const uint8 = new Uint8Array(buf)
  const uint16 = new Uint16Array(buf)  
  uint8[0] = typedArr[offset]
  uint8[1] = typedArr[offset + 1]

  return uint16[0]
}

read-stream-stateful.js

const buf = new ArrayBuffer(16)
const uint8 = new Uint8Array(buf)
const uint16 = new Uint16Array(buf)

export const readUint16 = (typedArr, offset) => {
  uint8[0] = typedArr[offset]
  uint8[1] = typedArr[offset + 1]
  
  return uint16[0]
}

test.js

const data = new Uint8Array(8)
data[0] = Math.pow(2, 0)
data[1] = Math.pow(2, 1)
data[2] = Math.pow(2, 2)
data[3] = Math.pow(2, 3)
data[4] = Math.pow(2, 4)
data[5] = Math.pow(2, 5)
data[6] = Math.pow(2, 6)
data[7] = Math.pow(2, 7)

console.time('letsgo')

for (let i = 0; i < 1000000; i++) {
  readUInt8(data, 0)
  readUInt16(data, 0)
  readUInt32(data, 0)
  readUInt8(data, 7)
  readUInt16(data, 6)
  readUInt32(data, 4)
  readFloat32(data, 0)
  readFloat32(data, 4)
  readFloat64(data, 0)
}


console.timeEnd('letsgo')