js时间格式化-不同时区

function getLocalDate(shijianchuo){
var instance =new Date(shijianchuo); //创建一个Date对象
var localTime = instance.getTime();
var localOffset=instance.getTimezoneOffset()*60000; //获得当地时间偏移的毫秒数
var utc = localTime + localOffset; //utc即GMT时间
var offset =8; //东8区
var beijing = utc + (3600000*offset);
return new Date(beijing);
}