How to update the active element on click?

[FrancescoMussi]

I need to change the active day when a day is clicked.
I thought I could do it by assign the day string to this.value when a day is clicked:

onDayClick3 (date, str) {
  this.date3 = str
  this.value = str
},

But it doesn't update the active day.

How can I do that?

Thanks