将javascript文件或blob编码和解码为base64

function encodeToBase64(file) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onloadend = () => {
      const base64Data = reader.result.split(',')[1];
      resolve(base64Data);
    };
    reader.onerror = reject;
    reader.readAsDataURL(file);
  });
}

// 使用示例
const fileInput = document.getElementById('fileInput');
fileInput.addEventListener('change', async (event) => {
  const file = event.target.files[0];
  const base64Data = await encodeToBase64(file);
  console.log(base64Data);
});

function decodeFromBase64(base64Data, mimeType) {
  const byteCharacters = atob(base64Data);
  const byteArrays = [];

  for (let i = 0; i < byteCharacters.length; i++) {
    byteArrays.push(byteCharacters.charCodeAt(i));
  }

  const byteArray = new Uint8Array(byteArrays);
  return new Blob([byteArray], { type: mimeType });
}

// 使用示例
const base64Data = '...'; // Base64编码的数据
const mimeType = 'image/jpeg'; // 数据的MIME类型
const blob = decodeFromBase64(base64Data, mimeType);
console.log(blob);