Vue.js + ES6: TodoMVCをつくる 04 ー チェックをまとめてオン/オフしたり削除する

<section class="todoapp">
	<header class="header">
		<h1>todos</h1>
		<input class="new-todo"
			autofocus
			autocomplete="off"
			placeholder="What needs to be done?"
			v-model="newTodo"
			@keypress.enter="addTodo">
	</header>
	<section class="main" v-show="todos.length" v-cloak>
		<input id="toggle-all" class="toggle-all" type="checkbox" v-model="allDone">
		<label for="toggle-all"></label>
		<ul class="todo-list">
			<li v-for="todo in filteredTodos"
				class="todo"
				:key="todo.id"
				:class="{completed: todo.completed}">
				<div class="view">
					<input class="toggle" type="checkbox" v-model="todo.completed">
					<label>{{todo.title}}</label>
					<button class="destroy" @click="removeTodo(todo)"></button>
				</div>
			</li>
		</ul>
	</section>
	<footer class="footer" v-show="todos.length" v-cloak>
		<span class="todo-count">
			<strong>{{remaining}}</strong> {{remaining | pluralize}} left
		</span>
		<ul class="filters">
			<li><a href="#/all" :class="{selected: visibility == 'all'}">All</a></li>
			<li><a href="#/active" :class="{selected: visibility == 'active'}">Active</a></li>
			<li><a href="#/completed" :class="{selected: visibility == 'completed'}">Completed</a></li>
		</ul>
		<button class="clear-completed" @click="removeCompleted" v-show="todos.length > remaining">
			Clear completed
		</button>
	</footer>
</section>

const STORAGE_KEY = 'todos-vuejs-2.0';
const todoStorage = {
	fetch() {
		const todos = JSON.parse(localStorage.getItem(STORAGE_KEY) || '[]');
		todos.forEach((todo, index) =>
			todo.id = index
		);
		todoStorage.uid = todos.length;
		return todos;
	},
	save(todos) {
		localStorage.setItem(STORAGE_KEY, JSON.stringify(todos));
	}
};
const filters = {
	all(todos) {
		return todos;
	},
	active(todos) {
		return todos.filter((todo) =>
			!todo.completed
		);
	},
	completed(todos) {
		return todos.filter((todo) =>
			todo.completed
		);
	}
};
const app = new Vue({
	data: {
		todos: todoStorage.fetch(),
		newTodo: '',
		visibility: 'all'
	},
	watch: {
		todos: {
			handler(todos) {
				todoStorage.save(todos);
			},
			deep: true
		}
	},
	computed: {
		filteredTodos() {
			return filters[this.visibility](this.todos);
		},
		remaining() {
			const todos = filters.active(this.todos);
			return todos.length;
		},
		allDone: {
			get() {
				return this.remaining === 0;
			},
			set(value) {
				this.todos.forEach((todo) =>
					todo.completed = value
				);
			}
		}
	},
	filters: {
		pluralize(n) {
			return n === 1 ? 'item' : 'items';
		}
	},
	methods: {
		addTodo() {
			const value = this.newTodo && this.newTodo.trim();
			if (!value) {
				return;
			}
			this.todos.push({
				id: todoStorage.uid++,
				title: value,
				completed: false
			});
			this.newTodo = '';
		},
		removeTodo(todo) {
			this.todos.splice(this.todos.indexOf(todo), 1);
		},
		removeCompleted() {
			this.todos = filters.active(this.todos);
		}
	}
});
function onHashChange() {
	const visibility = window.location.hash.replace(/#\/?/, '');
	if (filters[visibility]) {
		app.visibility = visibility;
	} else {
		window.location.hash = '';
		app.visibility = 'all';
	}
}
window.addEventListener('hashchange', onHashChange);
onHashChange();
app.$mount('.todoapp');