Vue.js - How to implement Computed properties on objects of array?

Question

I have an array of objects inside my Vue instance, and for each item I'd like to write a Computed property.

Each object has only two properties: firstName and lastName. I would like to write a Computed property for each named 'fullName', which is just a concatenation of firstName and lastName.

I'm familiar with implementing Computed properties of data object properties of a Vue instances, but when it comes to doing so with elements of an array, I get confused.

Currently, my code is this:

var app = new Vue({
  el: '#app',
  data: {
    names: [{
        firstName: 'Mike',
        lastName: 'McDonald',
        done: false
      },
      {
        firstName: 'Alex',
        lastName: 'Nemeth',
        done: false
      },
      {
        firstName: 'Nate',
        lastName: 'Kostansek',
        done: true
      },
      {
        firstName: 'Ivan',
        lastName: 'Wyrsta',
        done: true
      }
    ]
  },
  computed: {
    fullName: function(name) {
      return name.lastName + ', ' + name.firstName;
    }      
  }
  methods: {
    toggle: function(name) {
      name.done = !name.done;
    }
  }
});

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.js"></script>
<div id='app'>
  <ol>
    <li v-for='name in names'>
      <input type='checkbox' v-bind:checked='name.done' v-on:change='toggle(name)' />
      <span v-if='!name.done'>{{ fullName(name) }}</span>
      <del v-else>{{ fullName(name) }}</del>
    </li>
  </ol>
</div>

And here is the respective jsFiddle

Answer 1

You could use fullname as method instead of computed property in your case :

var app = new Vue({
  el: '#app',
  data: {
    names: [{
        firstName: 'Mike',
        lastName: 'McDonald',
        done: false
      },
      {
        firstName: 'Alex',
        lastName: 'Nemeth',
        done: false
      },
      {
        firstName: 'Nate',
        lastName: 'Kostansek',
        done: true
      },
      {
        firstName: 'Ivan',
        lastName: 'Wyrsta',
        done: true
      }
    ]
  },
  computed: {

  },
  methods: {
    fullName: function(name) {
      return name.lastName + ', ' + name.firstName;
    },
    toggle: function(name) {
      name.done = !name.done;
    }
  }
});

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.js"></script>
<div id='app'>
  <ol>
    <li v-for='name in names'>
      <input type='checkbox' v-bind:checked='name.done' v-on:change='toggle(name)' />
      <span v-if='!name.done'>{{ fullName(name) }}</span>
      <del v-else>{{ fullName(name) }}</del>
    </li>
  </ol>
</div>

Another solution is to loop through names array inside a computed property by concatenating firstname and lastname, after that return this array and loop through it in your template

var app = new Vue({
  el: '#app',
  data: {
    names: [{
        firstName: 'Mike',
        lastName: 'McDonald',
        done: false
      },
      {
        firstName: 'Alex',
        lastName: 'Nemeth',
        done: false
      },
      {
        firstName: 'Nate',
        lastName: 'Kostansek',
        done: true
      },
      {
        firstName: 'Ivan',
        lastName: 'Wyrsta',
        done: true
      }
    ]
  },
  computed: {
    fullNames() {
      return this.names.map(name => {
        let fl = {};
        fl.fname = name.firstName + ", " + name.lastName;
        fl.done = name.done;
        return fl;
      })
    }
  },
  methods: {
    fullName: function(name) {
      return name.lastName + ', ' + name.firstName;
    },
    toggle: function(name) {
      name.done = !name.done;
    }
  }
});

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.js"></script>
<div id='app'>
  <ol>
    <li v-for='name in fullNames'>
      <input type='checkbox' v-bind:checked='name.done' v-on:change='toggle(name)' />
      <span v-if='!name.done'>{{ name.fname }}</span>
      <del v-else>{{  name.fname  }}</del>
    </li>
  </ol>
</div>

Answer 2

You can't use the 'computed' with a parameter. Most probably you want to use a method:

example

<span>{{ fullName('Hi') }}</span>

methods: {
  fullName(param) {
      return `${this.param} ${this.firstName} ${this.lastName}`
  }
}