How to calculate the timestamp in JS is several months ago? For example: 1577808000

var t = 1577808000； //Timestamp (seconds)

Var ot = new date (t *1000); //Become a time object (the timestamp of js is milliseconds)

var oy = ot . get full year（）； //year

var om = ot . getmonth（）+ 1； //month

Var TT = new date (); //Today

var ty = TT . get full year（）； //Today's year

var TM = TT . getmonth（）+ 1； //Today's month

var GM =（ty-oy）* 12+（TM-om）； //A few months later

alert（ot . tolocaledatestring（）+“Today“+GM+“Months“）；