Date.prototype.diff = function(date){
  return (this.getTime() - date.getTime())/(24 * 60 * 60 * 1000);
}
// 构造两个日期，分别是系统时间和2013/04/08 12:43:45
var now = new Date();
var date = new Date('2013/04/08 12:43:45');
// 调用日期差方法，求得参数日期与系统时间相差的天数
var diff = now.diff(date);
// 打印日期差    now-data=?
console.log(diff);