Vue计算属性的学习笔记

<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:{ 
 //a computed getter 
 reversedMessage:function(){ 
  //'this' points to the vm instance 
  return this.message.split('').reverse().join('') 
 } 
 } 
}) 

<p>Reversed message:"{{reversedMessage}}"</p> 

//in component 
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> 

<script src="https://unpkg.com/axios@0.12.0/dist/axios.min.js"></script> 
<script src="https://unpkg.com/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) { 
  this.answer = 'Waiting for you to stop typing...' 
  this.getAnswer() 
 } 
 }, 
 methods: { 
 // _.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 
 // 学习更多关于 _.debounce function (and its cousin 
 // _.throttle), 参考: https://lodash.com/docs#debounce 
 getAnswer: _.debounce( 
  function () { 
  var vm = this 
  if (this.question.indexOf('?') === -1) { 
   vm.answer = 'Questions usually contain a question mark. ;-)' 
   return 
  } 
  vm.answer = 'Thinking...' 
  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 
   }) 
  }, 
  // 这是我们为用户停止输入等待的毫秒数 
  500 
 ) 
 } 
}) 
</script>