Share an example tutorial on the implementation principle of the image upload component (React + Node)

import React, { Component } from 'react'
import Upload from '../../components/FormControls/Upload/'

//......

render() {
  return (
    <p><Upload uri={&#39;http://jafeney.com:9999/upload&#39;} /></p>
  )
}

render() {
  return (
    <form action={this.state.uri} method="post" encType="multipart/form-data">
      <p className="ry-upload-box">
        <p className="upload-main">
          <p className="upload-choose">
            <input
              onChange={(v)=>this.handleChange(v)}
              type="file"
              size={this.state.size}
              name="fileSelect"
              accept="image/*"
              multiple={this.state.multiple} />
            <span ref="dragBox"
              onDragOver={(e)=>this.handleDragHover(e)}
              onDragLeave={(e)=>this.handleDragHover(e)}
              onDrop={(e)=>this.handleDrop(e)}
              className="upload-drag-area">
              或者将图片拖到此处
            </span>
          </p>
          <p className={this.state.files.length?
             "upload-preview":"upload-preview ry-hidden"}>
            { this._renderPreview();  // 渲染图片预览列表 }
          </p>
        </p>
        <p className={this.state.files.length?
           "upload-submit":"upload-submit ry-hidden"}>
           <button type="button"
             onClick={()=>this.handleUpload()}
             class="upload-submit-btn">
             确认上传图片
           </button>
        </p>
        <p className="upload-info">
          { this._renderUploadInfos();  // 渲染图片上传信息 }
        </p>
      </p>
    </form>
  )
}

_renderPreview() {
  if (this.state.files) {
    return this.state.files.map((item, idx) => {
      return (
        <p className="upload-append-list">
          <p>
            <strong>{item.name}</strong>
            <a href="javascript:void(0)" rel="external nofollow" 
              className="upload-delete"
              title="删除" index={idx}></a>
            <br/>
            <img src={item.thumb} className="upload-image" />
           </p>
           <span className={this.state.progress[idx]?
             "upload-progress":
             "upload-progress ry-hidden"}>
             {this.state.progress[idx]}
           </span>
         </p>
      )
    })
  } else {
    return null
  }
}

_renderUploadInfos() {
  if (this.state.uploadHistory) {
    return this.state.uploadHistory.map((item, idx) => {
      return (
        <p>
          <span>上传成功，图片地址是：</span>
          <input type="text" class="upload-url" value={item.relPath}/>
          <a href={item.relPath} target="_blank">查看</a>
         </p>
      );
    })
  } else {
    return null;
  }
}

onChange={(e)=>this.handleChange(e)}

e.preventDefault()
let target = event.target
let files = target.files
let count = this.state.multiple ? files.length : 1
for (let i = 0; i < count; i++) {
  files[i].thumb = URL.createObjectURL(files[i])
}
// 转换为真正的数组
files = Array.prototype.slice.call(files, 0)
// 过滤非图片类型的文件
files = files.filter(function (file) {
  return /image/i.test(file.type)
})

this.setState({files: this.state.files.concat(files)})

upload(file, idx) {
  return new Promise((resolve, reject) => {
    let xhr = new XMLHttpRequest()
    if (xhr.upload) {
      // 上传中
      xhr.upload.addEventListener("progress", (e) => {
        // 处理上传进度
        this.handleProgress(file, e.loaded, e.total, idx);
      }, false)
      // 文件上传成功或是失败
      xhr.onreadystatechange = (e) => {
        if (xhr.readyState === 4) {
          if (xhr.status === 200) {
          // 上传成功操作
          this.handleSuccess(file, xhr.responseText)
          // 把该文件从上传队列中删除
          this.handleDeleteFile(file)
          resolve(xhr.responseText);
         } else {
          // 上传出错处理 
          this.handleFailure(file, xhr.responseText)
          reject(xhr.responseText);
         }
      }
    }
    // 开始上传
    xhr.open("POST", this.state.uri, true)
    let form = new FormData()
    form.append("filedata", file)
    xhr.send(form)
  })
}

xhr.upload.addEventListener("progress", (e) => {
  // 处理上传进度
  this.handleProgress(file, e.loaded, e.total, i);
}, false)

handleProgress(file, loaded, total, idx) {
  let percent = (loaded / total * 100).toFixed(2) + '%';
  let _progress = this.state.progress;
  _progress[idx] = percent;
  this.setState({ progress: _progress }) // 反馈到DOM里显示
}

onDragOver={(e)=>this.handleDragHover(e)}
onDragLeave={(e)=>this.handleDragHover(e)}
onDrop={(e)=>this.handleDrop(e)}

handleDragHover(e) {
  e.stopPropagation()
  e.preventDefault()
}

handleDrop(e) {
  this.setState({progress:[]})
  this.handleDragHover(e)
  // 获取文件列表对象
  let files = e.target.files || e.dataTransfer.files
  let count = this.state.multiple ? files.length : 1
  for (let i = 0; i < count; i++) {
    files[i].thumb = URL.createObjectURL(files[i])
  }
  // 转换为真正的数组 
  files = Array.prototype.slice.call(files, 0)
  // 过滤非图片类型的文件
  files = files.filter(function (file) {
    return /image/i.test(file.type)
  })
  this.setState({files: this.state.files.concat(files)})
}

multiple = { true } // 开启多图上传 
size = { 50 }    // 一次最大上传数量（虽没有上限，为保证服务端正常，建议50以下）

handleUpload() {
  let _promises = this.state.files.map((file, idx) => this.upload(file, idx))
  Promise.all(_promises).then( (res) => {
    // 全部上传完成 
    this.handleComplete()
  }).catch( (err) => { console.log(err) })
}

res.header('Access-Control-Allow-Origin', '*');

function allowCross(res) {
  res.header('Access-Control-Allow-Origin', '*');  
  res.header('Access-Control-Allow-Headers', 'Content-Type, Content-Length, Authorization, Accept, X-Requested-With , yourHeaderFeild');
  res.header('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');
  res.header("X-Powered-By",' 3.2.1')
  res.header("Content-Type", "application/json;charset=utf-8");
}

router.options('*', function (req, res, next) {
  res.header('Access-Control-Allow-Origin', '*');
  res.header('Access-Control-Allow-Headers', 'Content-Type, Content-Length, Authorization, Accept, X-Requested-With , yourHeaderFeild');
  res.header('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');
  res.header("X-Powered-By",' 3.2.1')
  res.header("Content-Type", "application/json;charset=utf-8");
  next();
});

/*使用multiparty处理上传的图片*/
router.post('/upload', function(req, res, next) { 
  // 生成multiparty对象，并配置上传目标路径
  var form = new multiparty.Form({uploadDir: './public/file/'});
  // 上传完成后处理
  form.parse(req, function(err, fields, files) {
    var filesTmp = JSON.stringify(files, null, 2);
    var relPath = '';
    if (err) {
      // 保存失败 
      console.log('Parse error: ' + err);
    } else {
      // 图片保存成功！
      console.log('Parse Files: ' + filesTmp);
      // 图片处理
      processImg(files);
    }
  });
});

npm install gm --save

sudo apt-get install imagemagick
sudo apt-get install graphicsmagick --with-webp // 支持webp格式的图片

  brew install imagemagick
  brew install graphicsmagick --with-webp  // 支持webp格式的图片

function reSizeImage(paths, dstPath, size) {
  return new Promise(function(resolve, reject) {
    gm(dstPath)
    .noProfile()
    .resizeExact(size)
    .write('.' + paths[1] + '@' + size + '00.' + paths[2], function (err) {
      if (!err) {
        console.log('resize as ' + size + ' ok!')
        resolve()
      }
      else {
        reject(err)
      };
    });
  });
}

var _dateSymbol = new Date().toLocaleDateString().split('-').join('');
var _timeSymbol = new Date().getTime().toString();

gm(uploadedPath).size(function(err, size) {
  var dstPath = './public/file/' + _dateSymbol + _timeSymbol 
    + '_' + size.width + 'x' + size.height + '.' 
    + _img.originalFilename.split('.')[1];
  var _port = process.env.PORT || '9999';
    relPath = 'http://' + req.hostname + ( _port!==80 ? ':' + _port : '' ) 
    + '/file/' + _dateSymbol + _timeSymbol + '_' + size.width + 'x' 
    + size.height + '.' + _img.originalFilename.split('.')[1];
  // 重命名
  fs.rename(uploadedPath, dstPath, function(err) {
    if (err) {
      reject(err)
    } else {
      console.log('rename ok!');
    }
  });
});