#Vue js computed 和 v-bindclass 的应用场景
```
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css">
<style>
.completed{ color: green; text-decoration: line-through; }
</style>
<nav class="navbar navbar-default navbar-static-top">
<div class="container-fluid">
<!-- Brand and toggle get grouped for better mobile display -->
<div class="navbar-header">
<a class="navbar-brand" href="#">Vue js 2.0</a>
</div>
</div><!-- /.container-fluid -->
</nav>
<div class="container" id="app">
<div class="row">
<div class="col-md-8 col-md-offset-2">
<div class="panel panel-default">
<div class="panel-heading">Welcome Vue js 2.0 Tutorial</div>
<div class="panel-body">
<h1>{{ message }} {{ todoCount }}</h1>
<ul class="list-group">
<li class="list-group-item" v-bind:class="{ 'completed':todo.completed }" v-for="(todo, index) in todos">
{{ todo.title }}
<button class="btn btn-xs pull-right" v-bind:class="[todo.completed ? 'btn-danger' : 'btn-success']" v-on:click="toggleCompletion(todo)">{{ todo.completed ? 'undo' : 'completed' }}</button>
<button class="btn btn-warning btn-xs pull-right" v-on:click="deleteTodo(index)">Delete</button>
</li>
</ul>
<form v-on:submit.prevent="addTodo(newTodo)">
<div class="form-group">
<input type="text" class="form-control" placeholder="Add a new todo"
v-model="newTodo.title">
</div>
<div class="form-group">
<button class="btn btn-success" type="submit">Add Todo</button>
</div>
</form>
</div>
</div>
</div>
</div>
</div>
<script src="js/vue.js"></script>
<script>
new Vue({
el: '#app',
data: {
message: 'My Todos',
todos: [
{id: 1, title: 'Learn Vuejs', completed: false}
],
newTodo: {id: null, title: '', completed: false}
},
computed: {
todoCount(){
return this.todos.length;
}
},
methods: {
addTodo(newTodo){
this.todos.push(newTodo);
this.newTodo = {id: null, title: '', completed: false};
},
deleteTodo(index){
this.todos.splice(index, 1);
},
toggleCompletion(todo){
todo.completed = !todo.completed;
}
}
});
</script>
```
