js实现算法--割字符串

function fenGeString(str,num) { //每num位就添加一个逗号
        //先将str转换为数组
        var strToArr =str.split('');
        for (var i =num ;i<str.length;i+=num+1){
            strToArr.splice(i,0,',');
        }
        return strToArr.join('');
    }

    var str = 'abdhiedhjofe';
    console.log(fenGeString(str,3));//abd,hie,dhj,ofe