根据生日计算年龄的JS代码

function displayage( yr, mon, day, countunit, decimals, rounding ) {

    // Starter Variables
    today = new Date();
    yr = parseInt(yr);
    mon = parseInt(mon);
    day = parseInt(day);
    var one_day = 1000*60*60*24;
    var one_month = 1000*60*60*24*30;
    var one_year = 1000*60*60*24*30*12;
    var pastdate = new Date(yr, mon-1, day);
    var return_value = 0;

    finalunit = ( countunit == "days" ) ? one_day : ( countunit == "months" ) ? one_month : one_year;
    decimals = ( decimals <= 0 ) ? 1 : decimals * 10;

    if ( countunit != "years" ) {
        if ( rounding == "rounddown" )
            return_value = Math.floor ( ( today.getTime() - pastdate.getTime() ) / ( finalunit ) * decimals ) / decimals;
        else
            return_value = Math.ceil ( ( today.getTime() - pastdate.getTime() ) / ( finalunit ) * decimals ) / decimals;
    } else {
        yearspast = today.getFullYear()-yr-1;
        tail = ( today.getMonth() > mon - 1 || today.getMonth() == mon - 1 && today.getDate() >= day ) ? 1 : 0;
        return_value = yearspast + tail;
    }

    return return_value;

}