生命週期
有哪些鉤子
beforeCreate created beforeMount mounted beforeUpdate updated beforeDestroy destroyed
測試代碼
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>vue生命週期學習</title> <script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script> </head> <body> <div id="app"> <h1>{{message}}</h1> </div> </body> <script> var vm = new Vue({ el: '#app', data: { message: 'Vue的生命週期' }, template:"<h1>{{message +'這是在template中的'}}</h1>", render: function(createElement){ return createElement('h1', 'this is createElement') }, beforeCreate: function() { console.group('------beforeCreate創建前狀態------'); console.log("%c%s", "color:red" , "el : " + this.$el); //undefined console.log("%c%s", "color:red","data : " + this.$data); //undefined console.log("%c%s", "color:red","message: " + this.message) }, created: function() { console.group('------created創建完畢狀態------'); console.log("%c%s", "color:red","el : " + this.$el); //undefined console.log("%c%s", "color:red","data : " + this.$data); //已被初始化 console.log("%c%s", "color:red","message: " + this.message); //已被初始化 }, beforeMount: function() { console.group('------beforeMount掛載前狀態------'); console.log("%c%s", "color:red","el : " + (this.$el)); //已被初始化 console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); //已被初始化 console.log("%c%s", "color:red","message: " + this.message); //已被初始化 }, mounted: function() { console.group('------mounted 掛載結束狀態------'); console.log("%c%s", "color:red","el : " + this.$el); //已被初始化 console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); //已被初始化 console.log("%c%s", "color:red","message: " + this.message); //已被初始化 }, beforeUpdate: function () { console.group('beforeUpdate 更新前狀態===============》'); console.log("%c%s", "color:red","el1 : " + this.$el); console.log("%c%s", "color:red","el2 : " + this.$el.innerHTML); console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); console.log("%c%s", "color:red","message: " + this.message); }, updated: function () { console.group('updated 更新完成狀態===============》'); console.log("%c%s", "color:red","el3 : " + this.$el); console.log("%c%s", "color:red","el4 : " + this.$el.innerHTML); console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); console.log("%c%s", "color:red","message: " + this.message); }, beforeDestroy: function () { console.group('beforeDestroy 銷燬前狀態===============》'); console.log("%c%s", "color:red","el : " + this.$el); console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); console.log("%c%s", "color:red","message: " + this.message); }, destroyed: function () { console.group('destroyed 銷燬完成狀態===============》'); console.log("%c%s", "color:red","el : " + this.$el); console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); console.log("%c%s", "color:red","message: " + this.message) } }) </script> </html>
總結
- beforeUpdate可以監聽到data數據的變化，但view層還沒有被渲染。等到updated的時候view層纔會重新渲染，數據更新。
- beforeMount方法中$el還未被創建，這期間vue先後生成2份模板，所以在beforeMount之前只是虛擬的，並未真實存在，所以在mounted的時候纔是調用屬性和方法最好的時機
- 渲染的優先級：render函數->template選項->外部HTML