VUE的計(jì)算屬性和偵聽(tīng)器使用案例

<div id="example">
 {{ message.split('').reverse().join('') }}
</div>

<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: {
 // 計(jì)算屬性的 getter
 reversedMessage: function () {
 // `this` 指向 vm 實(shí)例 return this.message.split('').reverse().join('')
 }
 }
})
Original message: "Hello"
Computed reversed message: "olleH"

<p>Reversed message: "{{ reversedMessage() }}"</p>
// 在組件中
methods: {
 reversedMessage: function () { return this.message.split('').reverse().join('')
 }
}

computed: {
 now: function () { return Date.now()
 }
}

<div id="demo">{{ fullName }}</div>
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?yàn)?AJAX 庫(kù)和通用工具的生態(tài)已經(jīng)相當(dāng)豐富，Vue 核心代碼沒(méi)有重復(fù) -->
<!-- 提供這些功能以保持精簡(jiǎn)。這也可以讓你自由選擇自己更熟悉的工具。 -->
<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` 發(fā)生改變，這個(gè)函數(shù)就會(huì)運(yùn)行
 question: function (newQuestion, oldQuestion) {
 this.answer = 'Waiting for you to stop typing...'
 this.getAnswer()
 }
 },
 methods: {
 // `_.debounce` 是一個(gè)通過(guò) Lodash 限制操作頻率的函數(shù)。
 // 在這個(gè)例子中，我們希望限制訪問(wèn) yesno.wtf/api 的頻率
 // AJAX 請(qǐng)求直到用戶輸入完畢才會(huì)發(fā)出。想要了解更多關(guān)于
 // `_.debounce` 函數(shù) (及其近親 `_.throttle`) 的知識(shí)，
 // 請(qǐng)參考：https://lodash.com/docs#debounce
 getAnswer: _.debounce(
 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
  })
 },
 // 這是我們?yōu)榕卸ㄓ脩敉Ｖ馆斎氲却暮撩霐?shù) 500
 )
 }
})
</script>