代码如下：

const dataURL = canvas.toDataURL({
      format: "png",
      width: 400,
      height: 400,
});

const link = document.createElement("a");
link.download = new Date().getTime();

link.href = dataURL;
document.body.appendChild(link);
link.click();
document.body.removeChild(link);

结果虽然文件是下下来了，但是浏览器出现以下报错

解决方法，改成

const dataURL = canvas.toDataURL({
      format: "png",
      width: 400,
      height: 400,
});

const link = document.createElement("a");

let blob = dataURLtoBlob(dataURL);
let url = URL.createObjectURL(blob);


link.download = new Date().getTime();

link.href = url;
document.body.appendChild(link);
link.click();
document.body.removeChild(link);

// 将Base64字符串转换为Blob对象
function dataURLtoBlob(dataurl) {
    var arr = dataurl.split(',');
    var mime = arr[0].match(/:(.*?);/)[1];
    var bstr = atob(arr[1]);
    var n = bstr.length;
    var u8arr = new Uint8Array(n);
    while(n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], {type:mime});
}

简言之，就是把
link.href = dataURL;

改成
let blob = dataURLtoBlob(dataURL);
let url = URL.createObjectURL(blob);
link.href = url;