componentDidMount() {
    var code = "";
    var lastTime,nextTime;
    var lastCode,nextCode;
    window.addEventListener('keypress',function(e){
      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){
        console.log(code);
        code = ""
 
;
      }       
    })
  }

能用，反正懶得解釋= =