将OffscreenCanvas内容以PNG格式保存到磁盘上

// 创建OffscreenCanvas
const offscreenCanvas = new OffscreenCanvas(300, 200);
const offscreenCtx = offscreenCanvas.getContext('2d');

// 在OffscreenCanvas上绘制内容
offscreenCtx.fillStyle = 'red';
offscreenCtx.fillRect(0, 0, 300, 200);

// 创建新的Canvas
const canvas = document.createElement('canvas');
canvas.width = offscreenCanvas.width;
canvas.height = offscreenCanvas.height;
const ctx = canvas.getContext('2d');

// 将OffscreenCanvas内容绘制到新的Canvas上
ctx.drawImage(offscreenCanvas.transferToImageBitmap(), 0, 0);

// 将Canvas内容转换为DataURL格式的字符串
const dataURL = canvas.toDataURL('image/png');

// 将DataURL字符串转换为Blob对象
const blob = dataURLToBlob(dataURL);

// 创建下载链接
const link = document.createElement('a');
link.href = URL.createObjectURL(blob);
link.download = 'image.png';
link.click();

// 辅助函数：将DataURL字符串转换为Blob对象
function dataURLToBlob(dataURL) {
  const arr = dataURL.split(',');
  const mime = arr[0].match(/:(.*?);/)[1];
  const bstr = atob(arr[1]);
  let n = bstr.length;
  const u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new Blob([u8arr], { type: mime });
}