[Vuejs]-Add days to date using vuejs

The data property is design for storing variables, not invoking functions or adding logic like you’re trying to do.

Try computed property:

computed: {
  tomorrow() {
    const d = new Date()
    d.setDate(d.getDate() + 1)
    return d 
  }
}

And then in your template you can do {{ tomorrow }} or in your vue component this.tomorrow