vue中计算属性（computed）、methods和watched之间的区别

<p>原始数据：{{msg}}</p> 
<p>改变后的数据：{{changemsg}}</p> 
var vm=new Vue({ 
<span style="white-space:pre"> </span>el:"#example", 
 data:{ 
 <span style="white-space:pre"> </span>msg:"hello", 
<span style="white-space:pre"> </span>}, 
<span style="white-space:pre"> </span>computed:{ 
  changemsg:function(){ 
  return this.msg.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
 }
 }
})