[FE] Canvas 转图片并下载的方式

// Trans to image
const canvas = document.getElementsByTagName('canvas')[0]
const link = canvas.toDataURL('image/png')
const filename = 'xxx'

// Download
let oA = document.createElement('a');
oA.download = filename // 设置下载的文件名，默认是'下载'
oA.href = link;
document.body.appendChild(oA);
oA.click();
oA.remove();