利用Blob进行文件上传的完整步骤

 var data1 = "a";
 var blob1 = new Blob([data1]);
 console.log(blob1); //输出：Blob {size: 1, type: ""}
 
 var debug = {hello: "world"};
 var blob = new Blob([JSON.stringify(debug, null, 2)],{type : 'application/json'});
 console.log(blob) // 输出 Blob(22) {size: 22, type: "application/json"}
 
 // 创建一个8字节的ArrayBuffer，在其上创建一个每个数组元素为2字节的“视图”
 var abf = new ArrayBuffer(8)
 var abv = new Int16Array(abf)
 var bolb_ArrayBuffer = new Blob(abv, {type : 'text/plain'})
 console.log(bolb_ArrayBuffer) //输出 Blob(4) {size: 4, type: "text/plain"}

slice(start, end, contentType)

var data = "abcdef";
var blob1 = new Blob([data]);
var blob2 = blob1.slice(0,3);

console.log(blob1); //输出：Blob {size: 6, type: ""}
console.log(blob2); //输出：Blob {size: 3, type: ""}

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);
  }
 }
}

// file是要下载的文件（blob对象）
downloadHandler: function (file, fileName) {
 let link = document.createElement('a')
 link.href = window.URL.createObjectURL(file)
 link.download = fileName
 link.click()
 window.URL.revokeObjectURL(link.href)
 if (navigator.userAgent.indexOf('Firefox') > -1) {
 const a = document.createElement('a')
 a.addEventListener('click', function (e) {
  a.download = fileName
  a.href = URL.createObjectURL(file)
 })
 let e = document.createEvent('MouseEvents')
 e.initEvent('click', false, false)
 a.dispatchEvent(e)
 }
}

var x = new XMLHttpRequest();
x.responseType = 'blob';  // 返回一个blob对象