js中如何通过身份证号计算出生日期和年龄

在html中有如下标签

     身份证号：<input type="text" id="Gra_IDCard" onChange="IDCardChange()"/> <br/>
     出生日期：<input type="date" id="Gra_BirthDate"/> <br/>
     用户年龄：<input type="number" id="Gra_NameAge"/>

在js中方法

<script>
        //身份证改变事件（孕妇）
        var IDCardChange = function () {
            //获取身份证号
            var idCard = $('#Gra_IDCard').val();
            //判断身份证长度
            if (idCard.length == 18) {
                //获取计算后出生日期
                var birthDateStr = getBirthDate(idCard);
                //设置出生日期
                $('#Gra_BirthDate').val(birthDateStr);

                //获取当前的日期
                var nowDateStr = getNowDate();
                //获取计算后年龄(两个日期之间)
                var age = getAge(birthDateStr, nowDateStr);
                //设置年龄
                $('#Gra_Age').val(age);
            }
        }

       //根据身份证号计算出生日期
        var getBirthDate = function (IDCard)
        {
            //获取身份证号的年、月、日
            var year = IDCard.substring(6, 10);
            var month = IDCard.substring(10, 12);
            var day = IDCard.substring(12, 14);
            //拼接成出生日期
            var birthDate = year + '-' + month + '-' + day;
            return birthDate;
        }

        //根据两个日期计算年龄（是否过生日）
        var getAge = function (startDateStr, endDateStr)
        {
            //计算两个日期相差多少年
            var startDate = new Date(startDateStr);
            var endDate = new Date(endDateStr);
            var yearNum = endDate.getFullYear() - startDate.getFullYear();
            //获取两个日期（月+日）部分
            var sStr = startDateStr.substring(5, 10);
            var eStr = endDateStr.substring(5, 10);
            //判断两个日期大小
            //判断是否过生日
            if (new Date(sStr) <= new Date(eStr)) {
                return yearNum + 1;
            }
            else {
                return yearNum;
            }
        }

        ///获取当前日期
        var getNowDate = function () {
            var d = new Date();
            var year = d.getFullYear();
            var month = d.getMonth() + 1;
            var day = d.getDate();
            var dateStr = year + '-' + getFormatDate(month) + '-' + getFormatDate(day);
            return dateStr;
        }

         //格式化日期的月份或天数的显示（小于10，在前面增加0）
        function getFormatDate(value) {
            if (value == undefined || value == "") {
                return '';
            }
            var str = value;
            if (parseInt(value) < 10) {
                str = '0' + value;
            }
            return str;
        }
</script>

实现效果（改变身份证号时，带出出生日期和年龄）

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注：需引入jquery.min.js文件，保证jquery可用