Date.prototype.AddDays = function(days) {  
    this.setDate(this.getDate() + days);  
    return this;  
}  

Date.prototype.AddHours = function(hours) {  
    this.setHours(this.getHours() + hours);  
    return this;  
}  

Date.prototype.AddMilliseconds = function(milliseconds) {  
    this.setMilliseconds(this.getMilliseconds() + milliseconds);  
    return this;  
}  

Date.prototype.AddMinutes = function(minutes) {  
    this.setMinutes(this.getMinutes() + minutes, this.getSeconds(), this.getMilliseconds());  
    return this;  
}  

Date.prototype.AddMonths = function(months) {  
    this.setMonth(this.getMonth() + months, this.getDate());  
    return this;  
}  

Date.prototype.AddSeconds = function(seconds) {  
    this.setSeconds(this.getSeconds() + seconds, this.getMilliseconds());  
    return this;  
}  

Date.prototype.AddYears = function(years) {  
    this.setFullYear(this.getFullYear() + years);  
    return this;  
}