<div id="example">
 a={{ a }}, b={{ b }}
</div>

var vm = new Vue({ //之所以起名vm，是因为这其实是mvvm中的vm
 el: '#example',
 data: {
 a: 1
 },
 computed: {
 // 一个计算属性的 getter
 b: function () {
  // `this` 指向 vm 实例
  return this.a + 1
 }
 }
})

a=1,b=2

console.log(vm.b) // -> 2
vm.a = 3
console.log(vm.b) // -> 3

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

var vm = new Vue({
 data: {
 firstName: 'Foo',
 lastName: 'Bar',
 fullName: 'Foo Bar'
 }
})

vm.$watch('firstName', function (val) {
 this.fullName = val + ' ' + this.lastName
})

vm.$watch('lastName', function (val) {
 this.fullName = this.firstName + ' ' + val
})

var vm = new Vue({
 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]
 }
 }
}
// ...