js中保留小数处理方法

// num要处理的数据，retain保留几位
        function keepNum(num, retain) {
            num = Number(num);
            num = num.toFixed(retain+1).split(".");
            num = num[0] + "." + num[1].substring(0, retain);
            return num;
        }
        var num=keepNum(-0.1,6)
        console.log(num);