Javascript Date subtractDays(days)

Date.prototype.subtractDays = function(days) {
    var dat = new Date(this.valueOf());
    dat.setDate(dat.getDate() - days);//from  ww w  .j ava 2  s  .c o m
    return dat;
}

//subtract days from a date
Date.prototype.subtractDays=function(days){
    if (arguments.length===1){
        if (typeof days !== 'number') return;
        this.setDate(this.getDate() - days);
        return this;
    }/*from  w  w  w.  j a va  2  s.c o  m*/
    return this;
}