html,js获取扫码设备的输入内容

<script type="text/javascript"><!--

window.onload = function () {// 获取扫描的二维码内容
  var code = "";
  var lastTime, nextTime;
  var lastCode, nextCode;
  document.onkeypress = function (e) {
      nextCode = e.which;
      nextTime = new Date().getTime();

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

      lastCode = nextCode;
      lastTime = nextTime;
  }
  this.doscan = function () {
      this.onkeypress = function (e) {
          if (e.which == 13) {
              console.log(code);
              console.log(code.length);

               //后续代码

              code = "";
          }
      }
  }
  this.doscan();
};

  //--></script>