js 字符串反转的方法

 
function getNewId(nums,jsonObject){
    var fp_hm = jsonObject.FP_DM;
    if (nums > fp_hm.length) {
        console.log("输入长度大于字符串长度，程序中止");
        return null;
    }
    var sub_fp_hm = fp_hm.substr(fp_hm.length - nums);
    return getNewStr(sub_fp_hm);
}
function getNewStr(oldStr){
    var newStr = "";
    for(var i = oldStr.length - 1; i >= 0; i--){
        newStr += oldStr[i];
    }
    return newStr;
}
var newJson = new Object();
newJson.FP_HM = "123456789";
newJson.FP_DM = "18312711538";
var json = eval(newJson);
var result = getNewId(11, json);
console.log(result);