javascript中保持纵横比的base64图像降维

function resizeBase64Image(base64, maxWidth, maxHeight) {
  return new Promise((resolve) => {
    const img = new Image();
    img.src = 'data:image/jpeg;base64,' + base64;
    img.onload = () => {
      const aspectRatio = img.width / img.height;
      let newWidth = img.width;
      let newHeight = img.height;

      if (img.width > maxWidth) {
        newWidth = maxWidth;
        newHeight = newWidth / aspectRatio;
      }

      if (newHeight > maxHeight) {
        newHeight = maxHeight;
        newWidth = newHeight * aspectRatio;
      }

      const canvas = document.createElement('canvas');
      const ctx = canvas.getContext('2d');
      canvas.width = newWidth;
      canvas.height = newHeight;

      ctx.drawImage(img, 0, 0, newWidth, newHeight);
      const resizedBase64 = canvas.toDataURL('image/jpeg');

      resolve(resizedBase64);
    };
  });
}

// 调用示例
const base64Image = '...'; // 这里填入你的base64图像数据
const maxWidth = 500; // 设置最大宽度
const maxHeight = 500; // 设置最大高度

resizeBase64Image(base64Image, maxWidth, maxHeight).then((resizedBase64) => {
  console.log('Resized base64 image:', resizedBase64);
});