JavaScript中實現數據庫中的dateadd與datediff步骤，很實用的

SQLServer 中有两个非常好用的日期操作函数：DATEADD(即dateadd)用来给日期添加指定时间间隔，DATEDIFF(即datediff)用来返回两个日期的时间间隔。可惜的是JavaScript没有，最近在项目中经常需要调用这两个函数，没法子，只好自己来写一个。

DateAdd函数：
程序代码

function DateAdd(interval,number,date){
    switch(interval.toLowerCase()){
        case "y": return new Date(date.setFullYear(date.getFullYear()+number));
        case "m": return new Date(date.setMonth(date.getMonth()+number));
        case "d": return new Date(date.setDate(date.getDate()+number));
        case "w": return new Date(date.setDate(date.getDate()+7*number));
        case "h": return new Date(date.setHours(date.getHours()+number));
        case "n": return new Date(date.setMinutes(date.getMinutes()+number));
        case "s": return new Date(date.setSeconds(date.getSeconds()+number));
        case "l": return new Date(date.setMilliseconds(date.getMilliseconds()+number));
    }
}

DateDiff函数：
程序代码

function DateDiff(interval,date1,date2){
    var long = date2.getTime() - date1.getTime(); //相差毫秒
    switch(interval.toLowerCase()){
        case "y": return parseInt(date2.getFullYear() - date1.getFullYear());
        case "m": return parseInt((date2.getFullYear() - date1.getFullYear())*12 + (date2.getMonth()-date1.getMonth()));
        case "d": return parseInt(long/1000/60/60/24);
        case "w": return parseInt(long/1000/60/60/24/7);
        case "h": return parseInt(long/1000/60/60);
        case "n": return parseInt(long/1000/60);
        case "s": return parseInt(long/1000);
        case "l": return parseInt(long);
    }
}