导出HTML5 Canvas图片并上传服务器功能

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);