<div id="example">

  <p>Original message: "{{ message }}"</p>

  <p>Computed reversed message: "{{ reversedMessage }}"</p>

</div>

var vm = new Vue({

  el: '#example',

  data: {

    message: 'Hello'

  },

  computed: {

    // 计算属性的 getter

    reversedMessage: function () {

      // `this` 指向 vm 实例

      return this.message.split('').reverse().join('')

    }

  }

})

var vm = new Vue({

  el: '#demo',

  data: {

    firstName: 'Foo',

    lastName: 'Bar',

    fullName: 'Foo Bar'

  },

  watch: {

    firstName: function (val) {

      this.fullName = val + ' ' + this.lastName

    },

    lastName: function (val) {

      this.fullName = this.firstName + ' ' + val

    }

  }

})

var vm = new Vue({

  el: '#demo',

  data: {

    firstName: 'Foo',

    lastName: 'Bar'

  },

  computed: {

    fullName: function () {

      return this.firstName + ' ' + this.lastName

    }

  }

})

// ...

computed: {

  fullName: {

    // getter

    get: function () {

      return this.firstName + ' ' + this.lastName

    },

    // setter

    set: function (newValue) {

      var names = newValue.split(' ')

      this.firstName = names[0]

      this.lastName = names[names.length - 1]

    }

  }

}

<div id="watch-example">

  <p>

    Ask a yes/no question:

    <input v-model="question">

  </p>

  <p>{{ answer }}</p>

</div>

<!-- 因为 AJAX 库和通用工具的生态已经相当丰富，Vue 核心代码没有重复 -->

<!-- 提供这些功能以保持精简。这也可以让你自由选择自己更熟悉的工具。 -->

<script src="https://cdn.jsdelivr.net/npm/axios@0.12.0/dist/axios.min.js"></script>

<script src="https://cdn.jsdelivr.net/npm/lodash@4.13.1/lodash.min.js"></script>

<script>

var watchExampleVM = new Vue({

  el: '#watch-example',

  data: {

    question: '',

    answer: 'I cannot give you an answer until you ask a question!'

  },

  watch: {

    // 如果 `question` 发生改变，这个函数就会运行

    question: function (newQuestion, oldQuestion) {

      this.answer = 'Waiting for you to stop typing...'

      this.debouncedGetAnswer()

    }

  },

  created: function () {

    // `_.debounce` 是一个通过 Lodash 限制操作频率的函数。

    // 在这个例子中，我们希望限制访问 yesno.wtf/api 的频率

    // AJAX 请求直到用户输入完毕才会发出。想要了解更多关于

    // `_.debounce` 函数 (及其近亲 `_.throttle`) 的知识，

    // 请参考：https://lodash.com/docs#debounce

    this.debouncedGetAnswer = _.debounce(this.getAnswer, 500)

  },

  methods: {

    getAnswer: function () {

      if (this.question.indexOf('?') === -1) {

        this.answer = 'Questions usually contain a question mark. ;-)'

        return

      }

      this.answer = 'Thinking...'

      var vm = this

      axios.get('https://yesno.wtf/api')

        .then(function (response) {

          vm.answer = _.capitalize(response.data.answer)

        })

        .catch(function (error) {

          vm.answer = 'Error! Could not reach the API. ' + error

        })

    }

  }

})

</script>