base64图片压缩 js

您可以使用JavaScript中的canvas将图片压缩为base64格式。以下是一个示例代码：

function compressImage(file, maxWidth, maxHeight) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.readAsDataURL(file);
    reader.onload = function(event) {
      const img = new Image();
      img.src = event.target.result;
      img.onload = function() {
        const canvas = document.createElement('canvas');
        let width = img.width;
        let height = img.height;
        if (width > height) {
          if (width > maxWidth) {
            height *= maxWidth / width;
            width = maxWidth;
          }
        } else {
          if (height > maxHeight) {
            width *= maxHeight / height;
            height = maxHeight;
          }
        }
        canvas.width = width;
        canvas.height = height;
        const ctx = canvas.getContext('2d');
        ctx.drawImage(img, 0, 0, width, height);
        const compressedBase64 = canvas.toDataURL('image/jpeg', 0.7); // 压缩质量为0.7
        resolve(compressedBase64);
      };
    };
    reader.onerror = function(error) {
      reject(error);
    };
  });
}