js怎么获得系统当前的时间，要求是XXXX-XX-XX XX:XX:XX格式的

    window.onload = function(){
        var dates = new Date();
        var years = dates.getFullYear();
        var months = dates.getMonth()+1;
        var days = dates.getDate();
        var hours = dates.getHours();
        var mins =dates.getMinutes(); 
        var secs = dates.getSeconds();
        document.write(years+"-"+months+"-"+days+" "+hours+":"+mins+":"+secs);
        
    }
  

var date = new Date();
var dd = date.getFullYear()+"-" + formatDate(date.getMonth()+1) + "-" + formatDate(date.getDate());

var hours = date.getHours() < 10?(0 + date.getHours()) : date.getHours();
var minutes = date.getMinutes() < 10?(0 + date.getMinutes()) : date.getMinutes();
var seconds = date.getSeconds() < 10?(0 + date.getSeconds()) : date.getSeconds();

dd = dd + " " + hours + ":" + minutes + ":" + seconds;
alert(dd );

function formatDate(val){
var valFormate = val;
if(valFormate<10){
valFormate = "0"+valFormate;
}
return valFormate;
}