Read the magic number of a file

get-magic-number.ts

export async function getMagicNumber(file: File, signatureLength: number = 4) {
  return file
    .slice(0, signatureLength)
    .arrayBuffer()
    .then((buffer) =>
      Array.from(new Uint8Array(buffer))
        .map((byte) => byte.toString(16).padStart(2, '0'))
        .join('')
        .toUpperCase()
    );
}