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

window.onload = (e)=> {
    document.onkeydown = (e)=> {
    	let nextCode,nextTime = '';
    	let lastTime = this.lastTime;
    	let code = this.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
        this.nextCode = nextCode;
        this.lastTime = nextTime;
        this.code = code;
    	// 键入Enter
        if(e.which == 13) {
            // 判断 code 长度（这里就获取到条码值了，以下业务自由发挥）
           	code = $.trim(code)
            if (code.length == 13) {
                this.$message('A类条码:' + code);
            } else if (code.length == 23) {
				this.$message('B类条码:' + code);
            } else if (code.length == 0) {
				this.$message('请输入条码');
            } else{
            	this.$message('条码不合法：' + code);
            }
            //键入回车务必清空code值
        	this.code = ''
        	return false;
        }
    }
}