Javascript日期对象的dateAdd与dateDiff方法

Date.prototype.dateAdd = function(interval,number)
{
var d = this;
var k={'y':'FullYear', 'q':'Month', 'm':'Month', 'w':'Date', 'd':'Date', 'h':'Hours', 'n':'Minutes', 's':'Seconds', 'ms':'MilliSeconds'};
var n={'q':3, 'w':7};
eval('d.set'+k[interval]+'(d.get'+k[interval]+'()+'+((n[interval]||1)*number)+')');
return d;
}
Date.prototype.dateDiff = function(interval,objDate2)
{
var d=this, i={}, t=d.getTime(), t2=objDate2.getTime();
i['y']=objDate2.getFullYear()-d.getFullYear();
i['q']=i['y']*4+Math.floor(objDate2.getMonth()/4)-Math.floor(d.getMonth()/4);
i['m']=i['y']*12+objDate2.getMonth()-d.getMonth();
i['ms']=objDate2.getTime()-d.getTime();
i['w']=Math.floor((t2+345600000)/(604800000))-Math.floor((t+345600000)/(604800000));
i['d']=Math.floor(t2/86400000)-Math.floor(t/86400000);
i['h']=Math.floor(t2/3600000)-Math.floor(t/3600000);
i['n']=Math.floor(t2/60000)-Math.floor(t/60000);
i['s']=Math.floor(t2/1000)-Math.floor(t/1000);
return i[interval];
}