/*
 *   功能:實現VBScript的DateAdd功能.
 *   引數:interval,字串表示式，表示要新增的時間間隔.
 *   引數:number,數值表示式，表示要新增的時間間隔的個數.
 *   引數:date,時間物件.
 *   返回:新的時間物件.
 *   var now = new Date();
 *   var newDate = DateAdd( "d", 5, now);
 *---------------   DateAdd(interval,number,date)   -----------------
 */
function DateAdd(interval, number, date) {
    switch (interval) {
    case "y ": {
        date.setFullYear(date.getFullYear() + number);
        return date;
        break;
    }
    case "q ": {
        date.setMonth(date.getMonth() + number * 3);
        return date;
        break;
    }
    case "m ": {
        date.setMonth(date.getMonth() + number);
        return date;
        break;
    }
    case "w ": {
        date.setDate(date.getDate() + number * 7);
        return date;
        break;
    }
    case "d ": {
        date.setDate(date.getDate() + number);
        return date;
        break;
    }
    case "h ": {
        date.setHours(date.getHours() + number);
        return date;
        break;
    }
    case "m ": {
        date.setMinutes(date.getMinutes() + number);
        return date;
        break;
    }
    case "s ": {
        date.setSeconds(date.getSeconds() + number);
        return date;
        break;
    }
    default: {
        date.setDate(d.getDate() + number);
        return date;
        break;
    }
    }
}

var now = new Date();
// 加五天.
var newDate = DateAdd("d ", 5, now);
alert(newDate.toLocaleDateString())
// 加兩個月.
newDate = DateAdd("m ", 2, now);
alert(newDate.toLocaleDateString())
// 加一年
newDate = DateAdd("y ", 1, now);
alert(newDate.toLocaleDateString())