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;
        }
    }