Methods (ok)

C:\xampp\htdocs\html\src\App.vue

<template>
  <ul>
    <h2>{{title}}</h2>
    <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>
    <li v-for="task in tasks" :key="task.id">
      {{task.id}}. {{ task.name }}
    </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 = '';
    }
  }
}
</script>