Upload image to S3, generates unique name

S3Upload.js

var FileTransfer = require('@remobile/react-native-file-transfer');

var s3Conf = {  
  key: 'KEY',
  bucket: 'BUCKET_NAME',
  aws_url:  'https://BUCKET_NAME.REGION.amazonaws.com'
}

var guid =  (function() {
    function s4() {
      return Math.floor((1 + Math.random()) * 0x10000)
        .toString(16)
        .substring(1);
    }
    return function() {
      return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
        s4() + '-' + s4() + s4() + s4();
    };
  })();

var s3Upload = function(uri) {
  return new Promise((resolve, reject) => {
  let fileTransfer = new FileTransfer();

  var name = guid() + '.jpg';
  

    var opts = {
      fileName: name,
      headers: {
        'Content-Length': 10000000
      },
      params: {
          AWSAccessKeyId: s3Conf.key,
          filename: name,
          acl: 'public-read',
          key: name,
          policy: 'SIGNED POLICY',
          signature: 'SIGNATURE',
          'Content-Type': 'image/jpeg'
      }
    };
    
    fileTransfer.upload(
      uri,
      encodeURI(s3Conf.aws_url),
      () => resolve(s3Conf.aws_url + '/' + name),
      err => reject(err), opts);
  })
}

module.exports = s3Upload;