//index.js
Page({
 data: {
 text: "This is page data."
 },
 onLoad: function(options) {
 // Do some initialize when page load.
 },
 onReady: function() {
 // Do something when page ready.
 },
 onShow: function() {
 // Do something when page show.
 },
 onHide: function() {
 // Do something when page hide.
 },
 onUnload: function() {
 // Do something when page close.
 },
 // Event handler.
 viewTap: function() {
 this.setData({
  text: 'Set some data for updating view.'
 })
 }
})

<view>{{text}}</view>
<view>{{array[0].msg}}</view>

Page({
 data: {
 text: 'init data',
 array: [{msg: '1'}, {msg: '2'}]
 }
})

Page({
 viewTap: function() {
 console.log('view tap')
 }
})

<!--index.wxml-->
<view>{{text}}</view>
<button bindtap="changeText"> Change normal data </button>
<view>{{array[0].text}}</view>
<button bindtap="changeItemInArray"> Change Array data </button>
<view>{{obj.text}}</view>
<button bindtap="changeItemInObject"> Change Object data </button>
<view>{{newField.text}}</view>
<button bindtap="addNewField"> Add new data </button>

//index.js
Page({
 data: {
 text: 'init data',
 array: [{text: 'init data'}],
 object: {
  text: 'init data'
 }
 },
 changeText: function() {
 // this.data.text = 'changed data' // bad, it can not work
 this.setData({
  text: 'changed data'
 })
 },
 changeItemInArray: function() {
 // you can use this way to modify a danamic data path
 var changedData = {}
 var index = 0
 changedData['array[' + index + '].text'] = 'changed data'
 this.setData(changedData)
 },
 changeItemInObject: function(){
 this.setData({
  'object.text': 'changed data'
 });
 },
 addNewField: function() {
 this.setData({
  'newField.text': 'new data'
 })
 }
})