最近有点迷各种古书，然后从 www.shuge.org 下载了各种高清的印本，快成db狂魔了…上面也有人在各种平台上分享，不胜感激…只是有些平台可以免费看但是没法下载… 反正你都canvas了，撸下来自己珍藏…

于是让qwen写了一段代码：

write a javascript function to trigger download a picture from a canvas image data. i mean there is a canvas with sth painted. i’d like to have a function to get its image data and convert the raw data into for example png file data array and trigger downloading the file from memory.

function downloadCanvasImage(canvas, filename = 'canvas-image.png', format = 'png') {
    // Get the image data URL from the canvas
    const mimeType = format === 'png' ? 'image/png' : 'image/jpeg';
    const dataURL = canvas.toDataURL(mimeType);

    // Create a temporary link element
    const link = document.createElement('a');
    link.href = dataURL;
    link.download = filename;

    // Append the link to the body (required for Firefox)
    document.body.appendChild(link);

    // Programmatically click the link to trigger the download
    link.click();

    // Remove the link from the DOM
    document.body.removeChild(link);
}

之后

const list = document.querySelectorAll('canvas.<classname>');
for (let i = 0; i < list.length; i ++) {
   downloadCanvasImage(list[i], `page${i+1}.png`);
}

然后再一个 image-to-pdf 就可以变成pdf存档了。大书库又多了几百GB…

把各种迷信的命相卜书籍看完，大致了解了古代历法五行阴阳历干支历（圭表测影、十月历、六龙历…），易经卦象…开始再看一遍医书，启动第二遍理解…