Vue.filter('format Date', format Date)

First, you need to import the Vue library to use its features. This can be done by including the following line at the top of your file:

import Vue from 'vue';

Next, you need to define your filter function. In this case, the filter is called 'formatDate' and it takes two parameters: the date to be formatted and an optional format string. The function should return the formatted date.

function formatDate(date, format) {
  // Implementation of the date formatting logic
  // ...
  return formattedDate;
}

After defining the filter function, you can register it with Vue using the Vue.filter method. This method takes two arguments: the name of the filter ('formatDate') and the function that implements the filter logic ('formatDate').

Vue.filter('formatDate', formatDate);

Once the filter is registered, you can use it in your Vue templates. To apply the filter to a value, you can use the {{ value | filterName }} syntax. In this case, to format a date, you would use:

{{ myDate | formatDate }}

You can also pass additional arguments to the filter by separating them with colons. For example, if you want to pass a format string to the formatDate filter, you can use:

{{ myDate | formatDate('YYYY-MM-DD') }}

This is how you can define and use a filter in Vue.js using the Vue.filter method.