js 获取扫码枪输入数据

1、扫码枪相当于键盘输入设备，输入一连串数字后加一个enter键。但在实际开发中需要区分是扫描枪输入还是键盘用户输入，区别在于扫码枪输入很快。

	  let code = '';
      let lastTime, nextTime;
      let lastCode, nextCode;
      window.document.onkeypress = (e) => {
        if (window.event) { // IE
          nextCode = e.keyCode;
        } else if (e.which) { // Netscape/Firefox/Opera
          nextCode = e.which;
        }
        if (nextCode === 13) {
          if (code.length < 3) return; // 手动输入的时间不会让code的长度大于2，所以这里只会对扫码枪有

          console.log(code); // 获取到扫码枪输入的内容，做别的操作

          code = '';
          lastCode = '';
          lastTime = '';
          return;
        }
        nextTime = new Date().getTime();
        if (!lastTime && !lastCode) {
          code += e.key;
        }

        if (lastCode && lastTime && nextTime - lastTime > 30) { // 当扫码前有keypress事件时,防止首字缺失
          code = e.key;
        } else if (lastCode && lastTime) {
          code += e.key;
        }
        lastCode = nextCode;
        lastTime = nextTime;
      }