可靠地识别JavaScript中的文件对象，如哈希等

const fileInput = document.querySelector('input[type="file"]');
const file = fileInput.files[0];

const reader = new FileReader();
reader.onload = function(event) {
  const fileContent = event.target.result;
  // 处理文件内容
};
reader.readAsText(file);

const formData = new FormData();
formData.append('file', file);

fetch('/upload', {
  method: 'POST',
  body: formData
})
.then(response => {
  // 处理上传结果
})
.catch(error => {
  // 处理上传错误
});

// 将文件对象转换为ArrayBuffer
const reader = new FileReader();
reader.onload = function(event) {
  const arrayBuffer = event.target.result;

  // 计算哈希
  crypto.subtle.digest('SHA-256', arrayBuffer)
    .then(hash => {
      const hashArray = Array.from(new Uint8Array(hash));
      const hashHex = hashArray.map(byte => byte.toString(16).padStart(2, '0')).join('');
      console.log(hashHex);
    })
    .catch(error => {
      console.error(error);
    });
};
reader.readAsArrayBuffer(file);