js 获取当前时间前几天日期

/*
* 获取当前时间前几日数据，length为天数
* myGetDay(0) -- 今日
* 格式 2018-08-19
* */
myGetDay: function(length) {
var time = (new Date).getTime() - 24 * 60 * 60 * 1000 * length;
var yesday = new Date(time); // 获取的是前几天日期
yesday = yesday.getFullYear() + "-" + (yesday.getMonth()>= 9 ? (yesday.getMonth() + 1) : "0" + (yesday.getMonth() + 1)) + "-" +(yesday.getDate()> 9 ? (yesday.getDate()) : "0" + (yesday.getDate())); //字符串拼接转格式：例如2018-08-19
return yesday
}