<input type="file" id="file" />
<!-- 进度条 -->
<progress id="progress" value="0" max="100"></progress>
// 获取 input file 的 dom 对象
const inputFile = document.querySelector('#file');

// 监听 change 事件
inputFile.addEventListener('change', function() {
 // 使用 formData 装载 file
 const formData = new FormData();
 formData.append('file', this.files[0]);
 
 // 上传文件
 upload(formData);
})

const upload = ( formData ) => {
 const xhr = new XMLHttpRequest();
 // 监听文件上传进度
 xhr.upload.addEventListener('progress', function(e) {
 if (e.lengthComputable) {
 // 获取进度
 const progress = Math.round((e.loaded * 100) / e.total);
 
 document.querySelector('#progress').setAttribute('value', progress);
 }
 },false);
 
 // 监听上传完成事件
 xhr.addEventListener('load', ()=>{
 console.log(':smile:上传完成')
 }, false);
 
 xhr.open('post', 'http://127.0.0.1:3000/upload');
 xhr.send(formData); 
}

const upload = ( formData ) => {
 $.ajax({
 type: 'post',
 url: 'http://127.0.0.1:3000/upload',
 data: formData,
 // 不进行数据处理和内容处理
 processData: false,
 contentType: false,
 // 监听 xhr
 xhr: function() {
  const xhr = $.ajaxSettings.xhr();
  if (xhr.upload) {
  xhr.upload.addEventListener('progress', e => {
  const { loaded, total } = e;
  var progress = (loaded / total) * 100;
  document.querySelector('#progress').setAttribute('value', progress);
  },
  false
  );
  return xhr;
  }
 },
 success: function(response) {
  console.log('上传成功');
 }
 });
}

const upload = async ( formData ) => {

 let config = {
 // 注意要把 contentType 设置为 multipart/form-data
 headers: {
  'Content-Type': 'multipart/form-data'
 },
 
 // 监听 onUploadProgress 事件
 onUploadProgress: e => {
  const {loaded, total} = e;
  // 使用本地 progress 事件
  if (e.lengthComputable) {
  let progress = loaded / total * 100;
  document.querySelector('#progress').setAttribute('value', progress);
  }
 }
 };

 const { status } = await axios.post('http://127.0.0.1:3000/upload', formData, config);
 if (res.status === 200) {
  console.log('上传完成:grinning:');
 }
}

const Koa = require('koa');
const Router = require('@koa/router');
const koaBody = require('koa-body');
const path = require('path');
const fs = require('fs');
const cors = require('@koa/cors');

const app = new Koa();
const router = new Router();

router.all('/upload', async ctx => {
 // 处理文件上传 
 const res = await dealFile(ctx);

 res && (ctx.body = {
 status: 200,
 msg: 'complete'
 });
});

// 中间件部分
app.use(cors());
app.use(
 koaBody({
 multipart: true,
 formidable: {
 maxFileSize: 2000 * 1024 * 1024 //最大2G
 }
 })
);
app.use(router.routes());
app.use(router.allowedMethods());

app.listen(3000);

const dealFile = ctx => {
 const { file } = ctx.request.files;

 const reader = fs.createReadStream(file.path);
 const writer = fs.createWriteStream(
 // 文件上传到 image 文件夹中
 path.resolve(__dirname, './image', file.name)
 );

 return new Promise((resove, reject) => {
 
 reader.pipe(writer);
 
 reader.on('end', () => {
 resove(true);
 });
 
 reader.on('error', err => {
 throw err;
 })
 
 });
};