js 如何获取一周前当前时间

// 获取一周前当前时间
theDayBeforeWeek = function() {
    var now = new Date();
    var d = now.getTime();
    var result = new Date();
    result.setTime(d - 7 * 24 * 60 * 60 * 1000);
    return result;
};

// 获取当前系统时间
getNow = function() {
    return new Date().Format("yyyy-MM-dd hh:mm:ss");

};
//格式化时间
Date.prototype.Format = function (fmt) {  
    var o = {
        "M+": this.getMonth() + 1,  
        "d+": this.getDate(),  
        "h+": this.getHours(),  
        "m+": this.getMinutes(),
        "s+": this.getSeconds(),
        "q+": Math.floor((this.getMonth() + 3) / 3),
        "S": this.getMilliseconds()
    };
    if (/(y+)/.test(fmt)) fmt = fmt.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length));
    for (var k in o)
    if (new RegExp("(" + k + ")").test(fmt)) fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));
    return fmt;
};