<div id="app">
  <h1>{{ message }}</h1>
  <form v-on:submit.prevent="addNewTodo">
    <input type="text" v-model="todo.task">
    <button type="submit">Add todo</button>
  </form>

  <ul>
    <li v-for="todo in todos" :class="{ completed: todo.isActive }" @click="$set(todo, 'isActive', !todo.isActive)">
     {{ todo.task }} <span v-on:click="deleteTodo">{{ todo.delete }}</span>
    </li>
  </ul>
</div>

var app = new Vue({
  el: '#app',
  data: {
    message: 'List of things to do today',
    todos: [
      { task: 'Have breakfast', delete:'(x)'},
      { task: 'Go to the gym', delete:'(x)'},
      { task: 'Study Vuejs', delete:'(x)'}
    ],
    todo: {task: '', delete: '(x)'}
  },
  methods: {
    addNewTodo: function(){
      this.todos.push( this.todo );
    },
    deleteTodo: function(){
      this.todos.shift( this.todo )
    },
  }
});