Day of next or previous month

Let's find out the day of the week on the first of the previous month. To do this, subtract one from the current month:

let now = new Date();

let date = new Date(now.getFullYear(), now.getMonth() - 1, 1);
console.log(date.getDay());

Question: will there be a problem if the current month is January? After all, it has the number 0, and when subtracting one from it, we get minus the first month.

Determine what day of the week was a month ago on the same day of the month as today.