computed-properties.vue

<template>
  <h1>{{ title }}</h1>

  <h2>Add a new task</h2>
  <span>You have {{ allTasks }} {{ allTasks > 1 ? 'tasks' : 'task' }} at the moment</span>

  <div>
    <input type="text"
        v-model="newTask"
        placeholder="Add a new task"
    >

    <button
      @click="addTask"
      :disabled="newTask.length < 1"
    >
      Add task
    </button>
  </div>

  <div v-if="newTask.length > 0">
    <h3>New task preview</h3>
    <p>{{ newTask }}</p>
  </div>

  <ul>
    <li v-for="(task, index) in latest" :key="task.id">
        {{ index + 1 }}. {{ task.name }}

        <div v-if="task.finished">
            <button>Delete task</button>
        </div>
    </li>
  </ul>
</template>

<script>
export default {
  data() {
    return {
      title: 'My To Do App',
      newTask: '',
      tasks: [
        { id: 1, name: 'Learn Vue JS', finished: false },
        { id: 2, name: 'Build a Vue application', finished: false },
        { id: 3, name: 'Write an article about Vue JS', finished: false }
      ]
    }
  },
  methods: {
    addTask() {
      if (this.newTask.length < 1) return

      this.tasks.push({
        id: this.tasks.length + 1,
        name: this.newTask,
        finished: false
      });

      this.newTask = ''
    },
    removeTask(taskID) {
      this.tasks = this.tasks.filter(task => {
          return task.id !== taskID
      });
    },
    finishTask(task) {
      task.finished = !task.finished
    }
  },
  computed: {
    allTasks() {
        return this.tasks.length
    },
    latest() {
        return [...this.tasks].reverse()
    }
  }
}
</script>