时间格式化方法，输出格式：2019-06-20 11:30:50

formatDateTime(date){
    let y = date.getFullYear();
    let m = date.getMonth() + 1;
    m = m < 10 ? ('0' + m) : m;
    let d = date.getDate();
    d = d < 10 ? ('0' + d) : d;
    let h = date.getHours();
    h=h < 10 ? ('0' + h) : h;
    let minute = date.getMinutes();
    minute = minute < 10 ? ('0' + minute) : minute;
    let second=date.getSeconds();
    second=second < 10 ? ('0' + second) : second;
    return y + '-' + m + '-' + d+' '+h+':'+minute+':'+second;
}