JS把格林威治时间转换为北京标准时间

function fermitTime(time){
var now = new Date(time);
var year = now.getFullYear();
var mon = now.getMonth()+;
var date= now.getDate();
if(mon<){
mon = ''+mon;
};
if(date<){
date = ''+date;
}
var postDate = year+'-'+mon+'-'+date;
return postDate;
}

alert(fermitTime(‘格林威治时间字符串’));