function getDatetime() {
    var d = new Date();
    var year = d.getFullYear();
    var month = change(d.getMonth() + 1);
    var day = change(d.getDate());
    var hour = change(d.getHours());
    var minute = change(d.getMinutes());
    var second = change(d.getSeconds());
    
    function change(t) {
        if (t < 10) {
            return "0" + t;
        } else {
            return t;
        }
    }

    var time = year + '-' + month + '-' + day + ' ' 
            + hour + ':' + minute + ':' + second;

    return time;
}


console.log(getDatetime());
// 执行结果
// 2019-06-26 23:35:16