let code = '';
let lastTime,
  nextTime,
  lastCode,
  nextCode;


function scanEvent(e, cb) {
  nextCode = e.which;
  nextTime = new Date().getTime();

  if (lastCode != null && lastTime != null && nextTime - lastTime <= 30) {
    code += String.fromCharCode(lastCode);
  } else if (lastCode != null && lastTime != null && nextTime - lastTime > 100) {
    code = '';
  }

  lastCode = nextCode;
  lastTime = nextTime;
  if (e.which === 13) {
    cb(code);
    console.log('code', code);
    code = '';
  }
}

export { scanEvent };

class Sample extends React.Component{
  componentDidMount(){
    window.addEventListener('keypress', this.scanWrapper, false);
  }

  componentWillUnmount() {
    window.removeEventListener('keypress', this.scanWrapper, false);
  }

  scanWrapper(e) {
    scanEvent(e, (code) => {
      // to do something...
    });
  }
}