js实现获取时间并格式化输出

<button>show time</button>
<div>a time</div>
<p></p>
<script>
    function getDate() {
        var date = new Date();
        var year = date.getFullYear();
        var mon = date.getMonth() + 1;
        var date2 = date.getDate();
        var hours = date.getHours();

        var minu = date.getMinutes();
        var sec = date.getSeconds();
        // let day=date.getDay();
        mon = mon < 10 ? '0' + mon : mon;
        date2 = date2 < 10 ? '0' + date2 : date2;
        hours = hours < 10 ? '0' + hours : hours;
        minu = minu < 10 ? '0' + minu : minu;
        sec = sec < 10 ? '0' + sec : sec;

        return year + '-' + mon + '-' + date2 + '  ' + hours + ':' + minu + ':' + sec;
    }

    var btn = document.querySelector('button');
    var div = document.querySelector('div');
    btn.onclick = function () {
        div.innerText = getDate();
    }
    var p = document.querySelector('p');
    // while (true) {
    //     for (let i = 0; i < 100000000; i++) ;
    p.innerText = getDate();
    // for (let i = 0; i < 100000000; i++) ;
    }
</script>