[Vuejs]-Validating a date before today with VeeValidate

Try to use rules expression like object.

VeeValidate syntax:
https://baianat.github.io/vee-validate/guide/syntax.html

For example:

data: {
    validators: {
        BirthDate: {
            required: true,
            date_format: 'dd-MM-yyyy',
            before: this.changeDateFormat(new Date(Date.now()))
        }
    }
},
methods: {
   changeDateFormat(dateStr) {
      if (dateStr != null) {
        var date = new Date(dateStr)
        var newDate = ("00" + (date.getDate())).slice(-2) + '-' + ("00" + (date.getMonth() + 1)).slice(-2) + '-' +date.getFullYear()
        return newDate
      }
    return ''
   }
},

And your directive:

v-validate="validators.BirthDate"