function handleSave () {
        //导出base64格式的图片数据
        var mycanvas = document.getElementById("mycanvas");
        var base64Data = mycanvas.toDataURL("image/jpeg", 1.0);
        //封装blob对象
        var blob = dataURItoBlob(base64Data);
        //组装formdata
        var fd = new FormData();
        fd.append("fileData", blob);//fileData为自定义
        fd.append("fileName", "123jpg");//fileName为自定义，名字随机生成或者写死，看需求
        //ajax上传，ajax的形式随意，JQ的写法也没有问题
        //需要注意的是服务端需要设定，允许跨域请求。数据接收的方式和<input type="file"/> 上传的文件没有区别
        var xmlHttp = new XMLHttpRequest();
        xmlHttp.open("POST", “你发送上传请求的url”);
        xmlHttp.setRequestHeader("Authorization", 'Bearer ' + localStorage.token);//设置请求header,按需设定，非必须
        xmlHttp.send(fd);
        //ajax回调
        xmlHttp.onreadystatechange = () => {
            //todo  your code...
        };
    };
function dataURItoBlob (base64Data) {
    var byteString;
    if (base64Data.split(',')[0].indexOf('base64') >= 0)
        byteString = atob(base64Data.split(',')[1]);
    else
        byteString = unescape(base64Data.split(',')[1]);
    var mimeString = base64Data.split(',')[0].split(':')[1].split(';')[0];
    var ia = new Uint8Array(byteString.length);
    for (var i = 0; i < byteString.length; i++) {
        ia[i] = byteString.charCodeAt(i);
    }
    return new Blob([ia], {type: mimeString});
};

function b64ToUint8Array(b64Image) {
   var img = atob(b64Image.split(',')[1]);
   var img_buffer = [];
   var i = 0;
   while (i < img.length) {
      img_buffer.push(img.charCodeAt(i));
      i++;
   }
   return new Uint8Array(img_buffer);
}
var b64Image = canvas.toDataURL('image/jpeg');
var u8Image  = b64ToUint8Array(b64Image);
var formData = new FormData();
formData.append("image", new Blob([ u8Image ], {type: "image/jpg"}));
var xhr = new XMLHttpRequest();
xhr.open("POST", "/api/upload", true);
xhr.send(formData);