扫码枪是模拟键盘输入的

created() {
      var _this=this
      var codeString = "";
    //定时器每隔200ms 清空codeString
    //扫码枪读取的速度比手动输入的速度要快很多，这也可以作为区分扫码还是手动输入的条件
    var scanTimeer = setInterval(function() {
        var now = new Date().getTime();
        if (now - lastTime > 200) {
            codeString = "";
        }
    }, 200);
    var lastTime;
    var caseFormat = false;
    document.onkeydown = function(e) {
        var nextTime = new Date().getTime();
        var code = e.which;
        //shift键
        if (code == 16) {
            caseFormat = true;
        } else {
            if (caseFormat) {
                if (code >= 65 && code <= 90) {
                    //转小写
                    code = code + 32;
                } else if (code >= 97 && code <= 122) {
                    //转大写
                    code = code - 32;
                }
                caseFormat = false;
            }
            var char = String.fromCharCode(code);
            if (codeString == "") {             
            codeString += char;
            } else if (nextTime - lastTime <= 30) {
              codeString += char;
            }
        }
        lastTime = nextTime;
    };

      window.onkeydown=(function(e) {
        var nextTime1 = new Date().getTime();
        var lastTime1;
        if (e.which ==13){
            _this.onScanning(codeString.substring(0, codeString.length - 1)); 
            codeString = ""; 
        }
    })
    },
  },

onScanning(code){
      console.log(code)//获取到的条形码
    },