javascript - Vuejs 使用官网上面的例子

1.使用vuejs 官网上面的例子，在控制台中发现了错误了，

VM2369 vue.js:2658 [Vue warn]: Unknown custom element: - did you register the component correctly? For recursive components, make sure to provide the "name" option.
(found in root instance)

2.源码：

Vue.component('todo-item', {
  props: ['todo'],
  template: '
{{ todo.text }}
'
})
var app7 = new Vue({
  el: '#app-7',
  data: {
    groceryList: [
      { text: 'Vegetables' },
      { text: 'Cheese' },
      { text: 'Whatever else humans are supposed to eat' }
    ]
  }
})