SOURCE

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('')
    }
  }
})
// watch模式
var vm2 = 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
    }
  }
})

// 计算模式
var vm3 = new Vue({
  el: '#demo2',
  data: {
    firstName: 'Jim',
    lastName: 'Jackson'
  },
	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]
			}
		}
	}
})



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
        })
    }
  }
})

<div id="example">
  <p>Original message: "{{ message }}"</p>
  <p>Computed reversed message: "{{ reversedMessage }}"</p>
</div>

<div id="demo">{{ fullName }}</div>
<div id="demo2">{{ fullName }}</div>


<div id="watch-example">
  <p>
    Ask a yes/no question:
    <input v-model="question">
  </p>
  <p>{{ answer }}</p>
</div>