js把字符串(yyyymmdd)格式轉換成日期格式（yyyy-mm-dd）

var dateString = "20151208180700";
var pattern = /(\d{4})(\d{2})(\d{2})(\d{2})(\d{2})(\d{2})/;
var formatedDate = dateString.replace(pattern, '$1-$2-$3 $4:$5:$6');
alert(formatedDate);
console.log(formatedDate);