本人花费半年的时间总结的《Java面试指南》已拿腾讯等大厂offer，已开源在github ，欢迎star！
首先，每个Vue实例在被创建之前都要经过一系列的初始化过程,这个过程就是vue的生命周期。
所有的钩子
beforeCreate —-创建前状态
created — 创建完毕状态
beforeMount — 挂载前状态
mounted — 挂载结束状态
beforeUpdate
updated
beforeDestroy
destroyed
1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677
!DOCTYPE htmlhtml 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" titlevue生命周期学习/title script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"/script/headbody div id="app" h1/h1 /div/bodyscript var vm = new Vue({ el: '#app', data: { message: 'Vue的生命周期' }, beforeCreate: function() { console.group('------beforeCreate创建前状态------'); 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创建完毕状态------'); 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挂载前状态------'); 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.$data); //已被初始化 console.log("%c%s", "color:red","message: " + this.message); //已被初始化 }, mounted: function() { console.group('------mounted 挂载结束状态------'); console.log("%c%s", "color:red","el : " + this.$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 更新前状态===============》'); console.log("%c%s", "color:red","el : " + this.$el); console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); console.log("%c%s", "color:red","message: " + this.message); }, updated: function () { console.group('updated 更新完成状态===============》'); console.log("%c%s", "color:red","el : " + this.$el); console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); console.log("%c%s", "color:red","message: " + this.message); }, beforeDestroy: function () { console.group('beforeDestroy 销毁前状态===============》'); console.log("%c%s", "color:red","el : " + this.$el); console.log(this.$el); console.log("%c%s", "color:red","data : " + this.$data); console.log("%c%s", "color:red","message: " + this.message); }, destroyed: function () { console.group('destroyed 销毁完成状态===============》'); console.log("%c%s", "color:red","el : " + this.$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
然后运行可以看到到created的时候就停止了：
<img class="alignnone size-full wp-image-6992" src="https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151110938-1893086667.png" src="https://www.javazhiyin.com/wp-content/themes/mnews/images/post-loading.gif" alt="" width="764" height="285" srcset="https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151110938-1893086667.png 764w, https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151110938-1893086667-150x56.png 150w, https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151110938-1893086667-300x112.png 300w" sizes="(max-width: 764px) 100vw, 764px">
el: ‘#app’,
如果我们在后面继续调用vm.$mount(el),可以发现代码继续向下执行了
1
vm.$mount(el) //这个el参数就是挂在的dom接点
结果：
<img class="alignnone size-full wp-image-6993" src="https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151612012-1257673202.png" src="https://www.javazhiyin.com/wp-content/themes/mnews/images/post-loading.gif" alt="" width="560" height="78" srcset="https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151612012-1257673202.png 560w, https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151612012-1257673202-150x21.png 150w, https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151612012-1257673202-300x42.png 300w" sizes="(max-width: 560px) 100vw, 560px">
!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”
titlevue生命周期学习/title
script src=”https://cdn.bootcss.com/vue/2.4.2/vue.js"/script
/head
body
div id=”app”
!–html中修改的–
h1undefined这是在outer HTML中的/h1
/div
/body
script
var vm = new Vue({
el: ‘#app’,
template: “h1undefined这是在template中的/h1”, //在vue配置项中修改的
data: {
message: ‘Vue的生命周期’
}
/script
/html
那么将vue对象中template的选项注释掉后打印如下信息：
<img class="alignnone size-full wp-image-6994" src="https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151634932-1925201400.png" src="https://www.javazhiyin.com/wp-content/themes/mnews/images/post-loading.gif" alt="" width="699" height="106" srcset="https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151634932-1925201400.png 699w, https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151634932-1925201400-150x23.png 150w, https://www.javazhiyin.com/wp-content/uploads/2018/08/1258691-20180731151634932-1925201400-300x45.png 300w" sizes="(max-width: 699px) 100vw, 699px">
这下就可以想想什么el的判断要在template之前了~是因为vue需要通过el找到对应的outer template。
在vue对象中还有一个render函数，它是以createElement作为参数，然后做渲染操作，而且我们可以直接嵌入JSX.
123456
new Vue({
el: '#app',
render: function(createElement) {
return createElement('h1', 'this is createElement')
}
})new Vue({
el: ‘#app’,
render: function(createElement) {
return createElement(‘h1’, ‘this is createElement’)
}
})
可以看到页面中渲染的是：
所以综合排名优先级：
render函数选项 template选项 outer HTML.
3. beforeMount和mounted 钩子函数间的生命周期
可以看到此时是给vue实例对象添加**$el成员，并且替换掉挂在的DOM元素。因为在之前console中打印的结果可以看到beforeMount**之前el上还是undefined。
4. mounted
注意看下面截图：
在mounted之前h1中还是通过****进行占位的，因为此时还有挂在到页面上，还是JavaScript中的虚拟DOM形式存在的。在mounted之后可以看到h1中的内容发生了变化。
5. beforeUpdate钩子函数和updated钩子函数间的生命周期
当vue发现data中的数据发生了改变，会触发对应组件的重新渲染，先后调用beforeUpdate和updated钩子函数。我们在console中输入：
1
vm.message = '触发组件更新'
vm.message = ‘触发组件更新’
发现触发了组件的更新：
6.beforeDestroy和destroyed钩子函数间的生命周期
beforeDestroy钩子函数在实例销毁之前调用。在这一步，实例仍然完全可用。
destroyed钩子函数在Vue 实例销毁后调用。调用后，Vue 实例指示的所有东西都会解绑定，所有的事件监听器会被移除，所有的子实例也会被销毁。
