在javascript中验证除扩展名之外的pdf文件？

const fileInput = document.getElementById('file-input');
fileInput.addEventListener('change', (event) => {
  const file = event.target.files[0];
  const reader = new FileReader();
  reader.onload = (e) => {
    const fileContent = e.target.result;
    if (isPDF(fileContent)) {
      console.log('这是一个PDF文件');
    } else {
      console.log('这不是一个PDF文件');
    }
  };
  reader.readAsArrayBuffer(file);
});

function isPDF(fileContent) {
  const pdfHeader = new Uint8Array([0x25, 0x50, 0x44, 0x46]);
  const fileContentBytes = new Uint8Array(fileContent);
  for (let i = 0; i < pdfHeader.length; i++) {
    if (pdfHeader[i] !== fileContentBytes[i]) {
      return false;
    }
  }
  return true;
}