var blob = new Blob(dataArr:Array<any>, opt:{type:string});

Blob.slice(start:number, end:number, contentType:string)

var canvas = document.getElementById("canvas");
canvas.toBlob(function(blob){
    console.log(blob);
});

initUpload();

//初始化上传
function initUpload() {
    var chunk = 100 * 1024;   //每片大小
    var input = document.getElementById("file");    //input file
    input.onchange = function (e) {
        var file = this.files[0];
        var query = {};
        var chunks = [];
        if (!!file) {
            var start = 0;
            //文件分片
            for (var i = 0; i < Math.ceil(file.size / chunk); i++) {
                var end = start + chunk;
                chunks[i] = file.slice(start , end);
                start = end;
            }
            
            // 采用post方法上传文件
            // url query上拼接以下参数，用于记录上传偏移
            // post body中存放本次要上传的二进制数据
            query = {
                fileSize: file.size,
                dataSize: chunk,
                nextOffset: 0
            }

            upload(chunks, query, successPerUpload);
        }
    }
}

// 执行上传
function upload(chunks, query, cb) {
    var queryStr = Object.getOwnPropertyNames(query).map(key => {
        return key + "=" + query[key];
    }).join("&");
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "http://xxxx/opload?" + queryStr);
    xhr.overrideMimeType("application/octet-stream");
    
    //获取post body中二进制数据
    var index = Math.floor(query.nextOffset / query.dataSize);
    getFileBinary(chunks[index], function (binary) {
        if (xhr.sendAsBinary) {
            xhr.sendAsBinary(binary);
        } else {
            xhr.send(binary);
        }

    });

    xhr.onreadystatechange = function (e) {
        if (xhr.readyState === 4) {
            if (xhr.status === 200) {
                var resp = JSON.parse(xhr.responseText);
                // 接口返回nextoffset
                // resp = {
                //     isFinish:false,
                //     offset:100*1024
                // }
                if (typeof cb === "function") {
                    cb.call(this, resp, chunks, query)
                }
            }
        }
    }
}

// 每片上传成功后执行
function successPerUpload(resp, chunks, query) {
    if (resp.isFinish === true) {
        alert("上传成功");
    } else {
        //未上传完毕
        query.offset = resp.offset;
        upload(chunks, query, successPerUpload);
    }
}

// 获取文件二进制数据
function getFileBinary(file, cb) {
    var reader = new FileReader();
    reader.readAsArrayBuffer(file);
    reader.onload = function (e) {
        if (typeof cb === "function") {
            cb.call(this, this.result);
        }
    }
}

createDownload("download.txt","download file");

function createDownload(fileName, content){
    var blob = new Blob([content]);
    var link = document.createElement("a");
    link.innerHTML = fileName;
    link.download = fileName;
    link.href = URL.createObjectURL(blob);
    document.getElementsByTagName("body")[0].appendChild(link);
}