Vue 2.x computed property is not updated when its dependencies are binded with inline data

Question

I face the following problem trying to migrate from Vue 1.0.27 to Vue 2.0.1.

EDIT added working JSFidle

The situation:

I have built a very simple app that takes a list of tasks (from the model) and displays them in an un-ordered list, as well as the number of tasks that are not flagged as completed (i.e. remaining tasks). The code for the ViewModel and the Model is shown below:

 /*************
 *  ViewModel *
 * ***********/

var vm = new Vue({
    el: '#my-app',
    data: data
});


 /*************
 *    Model   *
 * ***********/

var data = {
    my_tasks: [
        {body: "Go to the doctor", completed: false},
        {body: "Go to the bank", completed: false},
        {body: "Go to the zoo", completed: false}
    ],
};

In order to display the list of tasks I use a <task-list> custom component. The component:

• Has a tasks property via props
• Has a computed property called remaining that calculates the number of the tasks that are not completed
• Has two methods toggleCompletedStatus and inProgress

The code for the custom component is shown below

 /*****************
 *    Component   *
 * ***************/

Vue.component('task-list', {
    template: '#task-list-template',
    props: ['tasks'],
    computed: {
        remaining: function () {
            return this.tasks.filter(
                this.inProgress
            ).length;
        }
    },
    methods: {
        /**
         * Toggle the completed status of a task
         * @param item
         */
        toggleCompletedStatus: function (item) {
            return item.completed = !item.completed;
        },
        /**
         * Returns true when task is in progress (not completed)
         * @param item
         */
        inProgress: function (item) {
            return !item.completed;
        }

    },
});

<template id="task-list-template">
    <div>
        <h3>My tasks list ( {{ remaining }} )</h3>
        <ul>
            <li v-for="task in tasks" @click="toggleCompletedStatus(task)">
                {{ task.body }}
            </li>
        </ul>
    </div>
</template>

Finally in my view I use v-bind directive to bind the component's tasks property with the data.

 /************
 *    View   * <-- works fine with both Vue 1.X and 2.x
 * **********/

div id="my-app">
    <task-list :tasks="my_tasks"></task-list>
</div>

The problem:

If I try to pass the task list inline, the computed property remaining is NOT updated when the user clicks on a task. (i.e when the task.completed property changes)

 /************
 *    View   * <-- works in Vue 1.x, NOT working with Vue 2.x
 * **********/

div id="my-app">
    <task-list :tasks="[{body: "Go to the doctor", completed: false}, {body: "Go to the bank", completed: false}, {body: "Go to the dentist", completed: false}]"></task-list>
</div>

The same problem exists if I try to pass data from the server. The example below is using Laravel 5.3 in the backend:

 /************
 *    View   * <-- works in Vue 1.x, NOT working with Vue 2.x
 * **********/

div id="my-app">
    <task-list :tasks="{{$tasks}}"></task-list> <!-- {{$tasks}} are the json encoded data from the server -->
</div>

Any help appreciated

Answer 1

It's a normal behaviour, I'll let you check the migration guide about the props: http://vuejs.org/guide/migration.html#Prop-Mutation-deprecated4

Here your example updated to work with Vue 2.0:

 /*****************
 *    Component   *
 * ***************/

Vue.component('task-list', {
    template: '#task-list-template',
    props: ['tasks-data'],
    data: function () {
    	return { tasks: [] };
    },
    computed: {
        remaining: function () {
            return this.tasks.filter(
                this.inProgress
            ).length;
        }
    },
    created: function () {
    	this.tasks = this.tasksData; // Set default properties
    },
    methods: {
        /**
         * Toggle the completed status of a task
         * @param item
         */
        toggleCompletedStatus: function (item) {
            return item.completed = !item.completed;
        },
        /**
         * Returns true when task is in progress (not completed)
         * @param item
         */
        inProgress: function (item) {
            return !item.completed;
        }
    }
});


 /*************
 *  ViewModel *
 * ***********/

new Vue({
    el: '#my-app'
});

<script src="https://unpkg.com/vue@2.0.1/dist/vue.js"></script>
<div id="my-app">
  <task-list :tasks-data="[{body: 'Hello all', completed: false},{body: 'Goodbye all', completed: false}]"></task-list> 
</div>

<!-- Template for custom component -->
<template id="task-list-template">
    <div>
        <h3>Remaining task {{ remaining }}</h3>
        <ul>
            <li v-for="task in tasks" @click="toggleCompletedStatus(task)">
                {{ task.body }}
            </li>
        </ul>
    </div>
</template>
  

As you can see, I set the tasks in data in the created hook so Vue can listen to the changes and update the template.