对于实现页面逻辑交互等效果，我们必须知晓vue的生命周期，才能愉快的玩耍，知道我们写的东西应该挂载到哪里，vue官方给出的api讲解的那叫一个简单啊，如下：
所有的生命周期钩子自动绑定this上下文到实例中，因此你可以访问数据，对属性和方法进行运算。这意味着你不能使用箭头函数来定义一个生命周期方法(例如created: () => this.fetchTodos())。这是因为箭头函数绑定了父上下文，因此this与你期待的 Vue 实例不同，this.fetchTodos的行为未定义。
下面附加一张生命周期图示
1 <!DOCTYPE html> 2 <html> 3 <head> 4 <title></title> 5 <meta charset="utf-8"> 6 <script type="text/javascript" src="https://cdn.jsdelivr.net/vue/2.1.3/vue.js"></script> 7 </head> 8 <body> 9 10 <div id="app"> 11 <p>{{ message }}</p> 12 </div> 13 14 <script type="text/javascript"> 15 var app = new Vue({ 16 el: '#app', 17 data: { 18 message: "this is a test" 19 }, 20 beforeCreate: function () { 21 console.group('beforeCreate 创建前状态===============》'); 22 console.log("%c%s", "color:red", "el : " + this.$el); //undefined 23 console.log("%c%s", "color:red", "data : " + this.$data); //undefined 24 console.log("%c%s", "color:red", "message: " + this.message) 25 }, 26 created: function () { 27 console.group('created 创建完毕状态===============》'); 28 console.log("%c%s", "color:red", "el : " + this.$el); //undefined 29 console.log("%c%s", "color:red", "data : " + this.$data); //已被初始化 30 console.log("%c%s", "color:red", "message: " + this.message); //已被初始化 31 }, 32 beforeMount: function () { 33 console.group('beforeMount 挂载前状态===============》'); 34 console.log("%c%s", "color:red", "el : " + (this.$el)); //已被初始化 35 console.log(this.$el); 36 console.log("%c%s", "color:red", "data : " + this.$data); //已被初始化 37 console.log("%c%s", "color:red", "message: " + this.message); //已被初始化 38 }, 39 mounted: function () { 40 console.group('mounted 挂载结束状态===============》'); 41 console.log("%c%s", "color:red", "el : " + this.$el); //已被初始化 42 console.log(this.$el); 43 console.log("%c%s", "color:red", "data : " + this.$data); //已被初始化 44 console.log("%c%s", "color:red", "message: " + this.message); //已被初始化 45 }, 46 beforeUpdate: function () { 47 console.group('beforeUpdate 更新前状态===============》'); 48 console.log("%c%s", "color:red", "el : " + this.$el); 49 console.log(this.$el); 50 console.log("%c%s", "color:red", "data : " + this.$data); 51 console.log("%c%s", "color:red", "message: " + this.message); 52 }, 53 updated: function () { 54 console.group('updated 更新完成状态===============》'); 55 console.log("%c%s", "color:red", "el : " + this.$el); 56 console.log(this.$el); 57 console.log("%c%s", "color:red", "data : " + this.$data); 58 console.log("%c%s", "color:red", "message: " + this.message); 59 }, 60 beforeDestroy: function () { 61 console.group('beforeDestroy 销毁前状态===============》'); 62 console.log("%c%s", "color:red", "el : " + this.$el); 63 console.log(this.$el); 64 console.log("%c%s", "color:red", "data : " + this.$data); 65 console.log("%c%s", "color:red", "message: " + this.message); 66 }, 67 destroyed: function () { 68 console.group('destroyed 销毁完成状态===============》'); 69 console.log("%c%s", "color:red", "el : " + this.$el); 70 console.log(this.$el); 71 console.log("%c%s", "color:red", "data : " + this.$data); 72 console.log("%c%s", "color:red", "message: " + this.message) 73 } 74 }) 75 </script> 76 </body> 77 </html>