公式的话直接判断如下：

if(DATEDELTA(TODAY(),-5)=a2,"5天","其它")

if(DATEDELTA(TODAY(),-5)>=a2,"5天之内","其它")

如果是js判断的话

var today = new Date();

// 将日期设置为5天前

var yesterday = new Date();

yesterday.setDate(today.getDate() - 5);

// 获取年月日

var year = yesterday.getFullYear();

var month = yesterday.getMonth() + 1; // 月份从0开始计数，所以要加1

var day = yesterday.getDate();

// 输出结果

console.log(year + '-' + (month < 10 ? '0' + month : month) + '-' + (day < 10 ? '0' + day : day));