生命总共分为8个阶段：
beforeCreate（创建前）,
created（创建后）,
beforeMount(载入前),
mounted（载入后）,
beforeUpdate（更新前）,
updated（更新后）,
beforeDestroy（销毁前）,
destroyed（销毁后）
然后用一个实例的demo 来演示一下具体的效果：
<div id=app>{{a}}</div>
<script type="text/javascript">
var myVue = new Vue({
el: "#app",
data: {
a: "Vue.js"
},
beforeCreate: function() {
console.log("创建前")
console.log(this.a)
console.log(this.$el)
},
created: function() {
console.log("创建之后");
console.log(this.a)
console.log(this.$el)
},
beforeMount: function() {
console.log("mount之前")
console.log(this.a)
console.log(this.$el)
},
mounted: function() {
console.log("mount之后")
console.log(this.a)
console.log(this.$el)
},
beforeUpdate: function() {
console.log("更新前");
console.log(this.a)
console.log(this.$el)
},
updated: function() {
console.log("更新完成");
console.log(this.a);
console.log(this.$el)
},
beforeDestroy: function() {
console.log("销毁前");
console.log(this.a)
console.log(this.$el)
console.log(this.$el)
},
destroyed: function() {
console.log("已销毁");
console.log(this.a)
console.log(this.$el)
}
});
</script>
