JS计算两个日期之间相差的年份

    //startDateStr(2017-02-22) endDateStr(2018-02-21)    function getDateYearSub(startDateStr, endDateStr) {        var day = 24 * 60 * 60 *1000;         var sDate = new Date(Date.parse(startDateStr.replace(/-/g, "/")));        var eDate = new Date(Date.parse(endDateStr.replace(/-/g, "/")));        //得到前一天(算头不算尾)        sDate = new Date(sDate.getTime() - day);        //获得各自的年、月、日        var sY  = sDate.getFullYear();             var sM  = sDate.getMonth()+1;        var sD  = sDate.getDate();        var eY  = eDate.getFullYear();        var eM  = eDate.getMonth()+1;        var eD  = eDate.getDate();        if(eY > sY && sM == eM && sD == eD) {            return eY - sY;        } else {            alert("两个日期之间并非整年，请重新选择");            return 0;        }    }