js日期 操作

//重写toString方法，将时间转换为Y-m-d H:i:s格式  
Date.prototype.toString = function(){  
    return this.getFullYear() + "-" + (this.getMonth()+1) + "-" + this.getDate() + " " + this.getHours() + ":" + this.getMinutes() + ":" + this.getSeconds();     
}  
//格式化时间字符串  
Date.prototype.toFormatString = function(format){  
    if(format == ""){  
        return this.toString();   
    }  
    var str = '';  
    str = format.replace(/Y|y/,this.getFullYear())  
                .replace(/M|m/,this.getMonth() + 1)  
                .replace(/D|d/,this.getDate())  
                .replace(/H|h/,this.getHours())  
                .replace(/I|i/,this.getMinutes())  
                .replace(/S|s/,this.getSeconds());  
    return str;               
}  
//在当前时间上添加年数  
Date.prototype.addYear = function(years){  
    var cyear = this.getFullYear();  
    cyear += years;  
    this.setYear(cyear);  
    return this;      
}  
//在当前时间上添加天数  
Date.prototype.addDay = function(days){  
    var cd = this.getDate();  
    cd += days;  
    this.setDate(cd);  
    return this;  
}  
//在当前时间上添加月数  
Date.prototype.addMonth = function(months){  
    var cm = this.getMonth();  
    cm += months;  
    this.setMonth(cm);    
    return this;  
}