Date对象扩展

近期做了一个POC，需要在浏览器端做一些日期的处理工作，除去其中跟公司产品相关的部分，其它的代码还是比较通用的，主要有两个功能：

1. 根据一个Date对象获取相对应的特殊时间点，比如一天、一个月或者一年的起止时间；
2. 在一个Date对象上加减相应的时间值

js 代码

/**
 * This file is a Date extension which can handle specified moments
 *

/**
 * set the Date object to a specific local moment
 * @param {enum} iMoment the specific moment, can reference those extened properties of Date.
 */
Date.prototype.setToLocalMoment=function(iMoment)
{
    switch (iMoment) {
        case Date.MOMENT_DATE_START:
            this.setHours(0,0,0,0);
            break;
        case Date.MOMENT_DATE_END:
            this.setHours(23,59,59,999);
            break;
        case Date.MOMENT_MONTH_START:
            this.setHours(0,0,0,0);
            this.setDate(1);
            break;
        case Date.MOMENT_MONTH_END:
            this.setHours(23,59,59,999);
            //can not get the last day of a month directly,
            //so set to the first day in next month, and minus one day.
            //numDate is start from 1, so 0 means the last day before 1st
            this.setMonth(this.getMonth()+1, 0);
            break;
        case Date.MOMENT_YEAR_START:
            this.setHours(0,0,0,0);
            //numMonth is start from 0, to 11, but numDate is from 1 to 31, weird
            this.setMonth(0, 1);
            break;
        case Date.MOMENT_YEAR_END:
            this.setHours(23,59,59,999);
            this.setMonth(11, 31);
            break;
        default:
    }
}

/**
 * plus the specific values to this Date object
 * All parameters are optional, if one of them is positive, it's plused, otherwise, it's minused.
 * @param {int} iYear
 * @param {int} iMonth
 * @param {int} iDate
 * @param {int} iHours
 * @param {int} iMinutes
 * @param {int} iSeconds
 * @param {int} iMilliseconds
 */
Date.prototype.plus=function(iYear,iMonth,iDate,iHours,iMinutes,iSeconds,iMs)
{
    var ilYear=this.getFullYear(); ilYear+=iYear?iYear:0;
    var ilMonth=this.getMonth(); ilMonth+=iMonth?iMonth:0;
    var ilDate=this.getDate(); ilDate+=iDate?iDate:0;
    var ilHours=this.getHours(); ilHours+=iHours?iHours:0;
    var ilMinutes=this.getMinutes(); ilMinutes+=iMinutes?iMinutes:0;
    var ilSeconds=this.getSeconds(); ilSeconds+=iSeconds?iSeconds:0;
    var ilMs=this.getMilliseconds(); ilMs+=iMs?iMs:0;
    var date=new Date();
    date.setFullYear(ilYear, ilMonth, ilDate);
    date.setHours(ilHours,ilMinutes, ilSeconds,ilMs);
    return date;
}
Date.prototype.minus=function(iYear,iMonth,iDate,iHours,iMinutes,iSeconds,iMs)
{
    return this.plus(-iYear,-iMonth,-iDate,-iHours,-iMinutes,-iSeconds,-iMs);
}
/**
 * extened properties of Date: to define a set of special moment
 */
Date.MOMENT_DATE_START=100;
Date.MOMENT_DATE_END=101;
Date.MOMENT_MONTH_START=110;
Date.MOMENT_MONTH_END=111;
Date.MOMENT_YEAR_START=120;
Date.MOMENT_YEAR_END=121;