JS 身份证号码验证

以下代码是从腾讯团购网站上提取的身份证号码验证，仅为学习参考之用。
（通过 http://jsbeautifier.org/ 进行代码格式化）

function checkIdcard(elem) {
    var area = {
        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 idcard = elem.toUpperCase();
    var Y, JYM;
    var S, M;
    var idcard_array = new Array();
    idcard_array = idcard.split("");
    if (area[parseInt(idcard.substr(0, 2))] == null) {
        return false;
    }
    switch (idcard.length) {
    case 15:
        if ((parseInt(idcard.substr(6, 2)) + 1900) % 4 == 0 || ((parseInt(idcard.substr(6, 2)) + 1900) % 100 == 0 && (parseInt(idcard.substr(6, 2)) + 1900) % 4 == 0)) {
            ereg = /^[1-9][0-9]{5}[0-9]{2}((01|03|05|07|08|10|12)(0[1-9]|[1-2][0-9]|3[0-1])|(04|06|09|11)(0[1-9]|[1-2][0-9]|30)|02(0[1-9]|[1-2][0-9]))[0-9]{3}$/;
        } else {
            ereg = /^[1-9][0-9]{5}[0-9]{2}((01|03|05|07|08|10|12)(0[1-9]|[1-2][0-9]|3[0-1])|(04|06|09|11)(0[1-9]|[1-2][0-9]|30)|02(0[1-9]|1[0-9]|2[0-8]))[0-9]{3}$/;
        }
        if (ereg.test(idcard)) {
            return true;
        } else {
            return false;
        }
        break;
    case 18:
        if (parseInt(idcard.substr(6, 4)) % 4 == 0 || (parseInt(idcard.substr(6, 4)) % 100 == 0 && parseInt(idcard.substr(6, 4)) % 4 == 0)) {
            ereg = /^[1-9][0-9]{5}(19|20)[0-9]{2}((01|03|05|07|08|10|12)(0[1-9]|[1-2][0-9]|3[0-1])|(04|06|09|11)(0[1-9]|[1-2][0-9]|30)|02(0[1-9]|[1-2][0-9]))[0-9]{3}[0-9Xx]$/;
        } else {
            ereg = /^[1-9][0-9]{5}(19|20)[0-9]{2}((01|03|05|07|08|10|12)(0[1-9]|[1-2][0-9]|3[0-1])|(04|06|09|11)(0[1-9]|[1-2][0-9]|30)|02(0[1-9]|1[0-9]|2[0-8]))[0-9]{3}[0-9Xx]$/;
        }
        if (ereg.test(idcard)) {
            S = (parseInt(idcard_array[0]) + parseInt(idcard_array[10])) * 7 + (parseInt(idcard_array[1]) + parseInt(idcard_array[11])) * 9 + (parseInt(idcard_array[2]) + parseInt(idcard_array[12])) * 10 + (parseInt(idcard_array[3]) + parseInt(idcard_array[13])) * 5 + (parseInt(idcard_array[4]) + parseInt(idcard_array[14])) * 8 + (parseInt(idcard_array[5]) + parseInt(idcard_array[15])) * 4 + (parseInt(idcard_array[6]) + parseInt(idcard_array[16])) * 2 + parseInt(idcard_array[7]) * 1 + parseInt(idcard_array[8]) * 6 + parseInt(idcard_array[9]) * 3;
            Y = S % 11;
            M = "F";
            JYM = "10X98765432";
            M = JYM.substr(Y, 1);
            if (M == idcard_array[17]) {
                return true;
            } else {
                return false;
            }
        } else {
            return false;
        };
        break;
    default:
        {
            return false;
        }
        break;
    }
    return true;
}