Vue js apply filter on v-model in an input field

I understand what you are trying to do, however, because of the two way binding when using v-model, it may be better to just format the date as you receive it from the server, and then, use it with the desired format in your front-end app ('DD/MM/YYYY').

When sending the data back to the back-end, you just format it back to the desired server format ('YYYY-MM-DD').

In your Vue app, the work flow would be something like this:

 new Vue({
    el: 'body',
    data: {
      date: null,
    },
    methods: {
        getDataFromServer: function() {
                // Ajax call to get data from server

                // Let's pretend the received date data was saved in a variable (serverDate)
                // We will hardcode it for this ex.
                var serverDate = '2015-06-26';

                // Format it and save to vue data property
                this.date = this.frontEndDateFormat(serverDate);
        },
        saveDataToServer: function() {
            // Format data first before sending it back to server
            var serverDate = this.backEndDateFormat(this.date);

            // Ajax call sending formatted data (serverDate)
        },
        frontEndDateFormat: function(date) {
            return moment(date, 'YYYY-MM-DD').format('DD/MM/YYYY');
        },
        backEndDateFormat: function(date) {
            return moment(date, 'DD/MM/YYYY').format('YYYY-MM-DD');
        }
    }
  });

This works well for me, hope it helps.

Here is a fiddle for it:

https://jsfiddle.net/crabbly/xoLwkog9/

Syntax UPDATE:

    ...
    methods: {
        getDataFromServer() {
                // Ajax call to get data from server

                // Let's pretend the received date data was saved in a variable (serverDate)
                // We will hardcode it for this ex.
                const serverDate = '2015-06-26'

                // Format it and save to vue data property
                this.date = this.frontEndDateFormat(serverDate)
        },
        saveDataToServer() {
            // Format data first before sending it back to server
            const serverDate = this.backEndDateFormat(this.date)

            // Ajax call sending formatted data (serverDate)
        },
        frontEndDateFormat(date) {
            return moment(date, 'YYYY-MM-DD').format('DD/MM/YYYY')
        },
        backEndDateFormat(date) {
            return moment(date, 'DD/MM/YYYY').format('YYYY-MM-DD')
        }
    }
  })

I had a similar problem when I wanted to uppercase an input value.

This is what I ended up doing:

// create a directive to transform the model value
Vue.directive('uppercase', {
  twoWay: true, // this transformation applies back to the vm
  bind: function () {
    this.handler = function () {
      this.set(this.el.value.toUpperCase());
    }.bind(this);
    this.el.addEventListener('input', this.handler);
  },
  unbind: function () {
    this.el.removeEventListener('input', this.handler);
  }
});

Then I can use this directive on the input field with a v-model.

<input type="text" v-model="someData" v-uppercase="someData">

Now, whenever I type into this field or change someData, the value is transformed to uppercase.

This essentially did the same thing as I hoped v-model="someData | uppercase" would do. But of course, you can't do that.

In summation: make a directive that transforms the data, not a filter.

Go to main.js and add the following code :

import moment from 'moment'
Vue.filter('myDate', function (value) {
    if (value) {
        return moment(String(value)).format('dd/mm/yyyy')
    }
});

In your HTML do the following :

<label>Date</label>
<v-text-field :value="date | myDate" @input="value=>date=value"></v-text-field>
<p>{{ date | myDate 'dd/mm/yyyy' }}</p>

So we used above v-bind to bind the value and @input event handler to have the v-model functionality.