js获取USB扫码枪数据

前言

1. 找了很多相关的教程不太好用，汲取各家之长总结精简了一下

原理

1. 扫码枪扫描到的条形码每一位会触发一次onkeydown事件
   比如扫描条码位‘1234567890’的条形码，会连续执行10次onkeydown事件
2. 条码扫描到最后一位，会直接触发Enter

代码

需要引入jQuery，我这里用的是vue框架，使用可按需修改方法that.data部分

window.onload = function(e) {
    document.onkeydown = (e)=> {
        let nextCode,nextTime = '';
        let lastTime = that.lastTime;
        let code = that.code;
        if (window.event) {// IE
            nextCode = e.keyCode
        } else if (e.which) {// Netscape/Firefox/Opera
            nextCode = e.which
        }
        nextTime = new Date().getTime();
        //字母上方 数字键0-9 对应键码值 48-57; 数字键盘 数字键0-9 对应键码值 96-105
        if((nextCode>=48&&nextCode<=57)  || (nextCode>=96&&nextCode<=105)){
            let codes = {'48':48,'49':49,'50':50,'51':51,'52':52,'53':53,'54':54,'55':55,'56':56,'57':57,
             '96':48,'97':49,'98':50,'99':51,'100':52,'101':53,'102':54,'103':55,'104':56,'105':57
            };
            nextCode = codes[nextCode];
            nextTime = new Date().getTime();
        }
        // 第二次输入延迟两秒，删除之前的数据重新计算
        if(nextTime && lastTime && nextTime-lastTime>2000){
            code = String.fromCharCode(nextCode);
        }else{
            code += String.fromCharCode(nextCode)
        }
        // 保存数据
        that.nextCode = nextCode;
        that.lastTime = nextTime;
        that.code = code;
        // 键入Enter
        if(e.which == 13) {
            // 判断 code 长度（这里就获取到条码值了，以下业务*发挥）
            code = $.trim(code)
            if (code.length == 13) {
                that.$message('A类条码:' + code);
            } else if (code.length == 23) {
                that.$message('B类条码:' + code);
            } else if (code.length == 0) {
                that.$message('请输入条码');
            } else{
                that.$message('条码不合法：' + code);
            }
            //键入回车务必清空code值
            that.code = ''
            return false;
        }
    }
}