Rule Definition
When the value of data is an object, it’s shared across all instances of a component. We might want to reuse this component, allowing users to maintain multiple lists (e.g. for shopping, wishlists, daily chores, etc). Since every instance of the component references the same data object, changing the title of one list will also change the title of every other list. The same is true for adding/editing/deleting a todo. Instead, we want each component instance to only manage its own data. For that to happen, each instance must generate a unique data object.

Remediation
Ensure to return objects from data properties

Violation Code Sample

Vue.component('some-comp', {
  data: {
    foo: 'bar'
  }
})

Fixed Code Sample

Vue.component('some-comp', {
  data: function () {
    return {
      foo: 'bar'
    }
  }
})

https://vuejs.org/v2/style-guide/#Component-data-essential