VUE 计算属性和侦听器 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>计算属性和侦听器</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
</head>
<body>
        <div id="app">
                <p>Original message: "{{ message }}"</p>
                <p>Computed reversed message: "{{ reversedMessage__() }}"</p>
        </div>
        <div id="watch-example">
            <p>
                Ask a yes/no question:
                <input v-model="question">
            </p>
            <p>{{ answer }}</p>
        </div>
</body>
</html>
<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>

<script>
    var vm = new Vue({
        el: '#app',
        data: {
            message: 'Hello'
        },
        computed: {
            // 计算属性的 getter
            reversedMessage: function () {
            // `this` 指向 vm 实例
                return this.message.split('').reverse().join('')
            },
            //显示的增加计算属性的set 和 get 方法
            /* 比较神奇的是 如果get方法中用到了data里面的属性 如果data里面属性变更则计算属性会跟着变 */
            reversedMessage_: {
                get: function () {
                    return this.message.split('').reverse().join('')+ '-max-'
                },
                set: function (v) {
                    return this.message + 'rand'
                }
            }
        },
        methods: {
            reversedMessage__ :function(){
                return this.message.split('').reverse().join('')+ Date.now()
            }
        },
    })

   
    console.log(vm);
</script>

 

posted @ 2019-03-04 11:46  鱼尾纹  阅读(298)  评论(0)  编辑  收藏  举报