Javascript canvas -从加载的4波段RGB图像到3波段JPEG图像中删除alpha？

var image = new Image();
image.src = 'image_url';
image.onload = function() {
  // 图像加载完成后的处理逻辑
};

var canvas = document.createElement('canvas');
canvas.width = image.width;
canvas.height = image.height;

var context = canvas.getContext('2d');
context.drawImage(image, 0, 0);

var imageData = context.getImageData(0, 0, canvas.width, canvas.height);

var data = imageData.data;
for (var i = 0; i < data.length; i += 4) {
  data[i + 3] = 255; // 设置alpha通道为255
}

var newImageData = context.createImageData(imageData.width, imageData.height);

var newData = newImageData.data;
for (var i = 0; i < data.length; i += 4) {
  newData[i] = data[i];
  newData[i + 1] = data[i + 1];
  newData[i + 2] = data[i + 2];
  newData[i + 3] = data[i + 3];
}

context.putImageData(newImageData, 0, 0);

var jpegDataURL = canvas.toDataURL('image/jpeg');