How can I set a date in the current day?

I imagine you are using the datepicker of element-ui

What I would do is:

• Define the properties date_start and date_end as computed
• When changing its values, in setter execute ifSameDay as method, not as property computed .
• In the setter of date_start and date_end fixed the value of this.form.dates[0] and this.form.dates[1] , since defining nested properties as computed is a problem. The getter of those two properties, in turn, returns the values of this.form.dates .
• When executing ifSameDay , if the condition is met, set this.form.date_reincorporation to the date you want, and set a property this.reincorporation_readonly as true to block the input.
• If the condition is not met, clean this.form.date_reincorporation and define this.reincorporation_readonly as false .

The input of the reincorporation date would be:

And you save yourself wrapping the parent in a v-if.

If your component today has the structure (I'm going to simplify a lot)

{
  name: 'Licencias',
  data() {
    return {
      form: {
        dates: [new Date(), new Date()],
        date_reincorporation: new Date()
      }
    }
  },
  methods: {
    ifSameDay() {
      const date_start = moment(this.form.dates[0]).format('DD/MM/YYYY');
      const date_end = moment(this.form.dates[1]).format('DD/MM/YYYY');
      return (date_start === date_end && date_start !== 'Invalid date') ? true : false;
    },
  }
};

With my suggestion, it would be:

{
  name: 'Licencias',
  data() {
    return {
      reincorporation_readonly: false,
      form: {
        dates: [new Date(), new Date()],
        date_reincorporation: new Date()
      }
    }
  },
  computed: {
    date_start: {
      get() {
        return this.form.dates[0];
      },
      set(date_start) {
        this.form.dates[0] = date_start;
        this.ifSameDay();
      },
    },
    date_end: {
      get() {
        return this.form.dates[1];
      },
      set(date_start) {
        this.form.dates[1] = date_end;
        this.ifSameDay();
      },
    },
  },
  methods: {
    ifSameDay() {
      const date_start = moment(this.form.dates[0]).format('DD/MM/YYYY');
      const date_end = moment(this.form.dates[1]).format('DD/MM/YYYY');
      if (date_start === date_end && date_start !== 'Invalid date') {
        this.form.date_reincorporation = date_end;
        this.reincorporation_readonly = true;
      }
    },
  }
};

In other words, the v-model of the start date and end date point to date_start and date_end , which modify indirectly this.form.dates . The funny thing is that by putting you getters and setters you can trigger the collateral effect of checking ifSameDay in which you set the reincorporation date and leave the input as readonly. In this case, there is no v-if in el-form-item .

This is just a possible approach. You could also add a watcher to the properties, but that seems dirtier to me.

Finally, you could also force the reincorporation date by submitting without touching the rest of your code, but you would have to do two checks:

submitForm() {

    this.form.date_reincorporation = this.ifSameDay? this.form.date[1] : this.form.date_reincorporation;

    this.form.date_reincorporation = this.form.date_reincorporation?  moment(this.form.date_reincorporation).format('YYYY-MM-DD HH:mm') : null; 

}