表明身份程序制度的主要目的是什么?

给你一段判断身份证的Js代码吧，这个我用过的，比较好用。
function f_check_IDno(obj)
{
var aCity={11:"北京",12:"天津",13:"河北",14:"山西",15:"内蒙古",21:"辽宁",22:"吉林",23:"黑龙江",31:"上海",32:"江苏",33:"浙江",34:"安徽",35:"福建",36:"江西",37:"山东",41:"河南",42:"湖北",43:"湖南",44:"广东",45:"广西",46:"海南",50:"重庆",51:"四川",52:"贵州",53:"云南",54:"西藏",61:"陕西",62:"甘肃",63:"青海",64:"宁夏",65:"新疆",71:"台湾",81:"香港",82:"澳门",91:"国外"};
var iSum = 0;
var info = "";
var strIDno = obj.value;
var idCardLength = strIDno.length;
if(!/^\d{17}(\d|x)$/i.test(strIDno)&&!/^\d{15}$/i.test(strIDno))
{