<span id="sp"> {{ msg }} </span>
<input type="button" value=" change data Value " @click="changeData">

 el: "#app",
data: {
msg: "hello Vue.js!",
},
methods: {
changeData() {
// this.msg = "Vue.js niubility!";
this.msg = Math.random();
}
},
// ==================== Initialization phase ====================
// 1. The first function in the life cycle , When the function is executed Vue The instance only completes the binding of its own events and the initialization of the life cycle function ,Vue There is no in the instance Data el methods Related properties
beforeCreate() {
console.log("beforeCreate: " + this.msg);
},
// 2. The second function in the life cycle , When the function is executed Vue The instance has been initialized data Properties and methods The related methods in this paper are as follows
created() {
console.log("created:" + this.msg);
},
// 3. The third function in the lifecycle , When the function is executed Vue take El The scope specified in is compiled as a template
beforeMount() {
console.log("beforeMount: " + document.getElementById("sp").innerText);
},
// 4. The fourth function in the life cycle , During the execution of this function , The data has been rendered into the interface and the page has been updated
mounted() {
console.log("Mounted: " + document.getElementById("sp").innerText);
},
// ==================== Operation phase ====================
// 5. The fifth function in the life cycle , The function is data Execute when the data in changes When this event is executed, it is just Vue In the example data The data change page still shows the original data
beforeUpdate() {
console.log("beforeUpdate-vue: " + this.msg);
console.log("beforeUpdate-dom: " + document.getElementById("sp").innerText);
},
// 6. The sixth function in the life cycle , When this function executes data Data changes in , The data in the page has also changed The data in the page has been and data The data in the are consistent
updated() {
console.log("updated-vue: " + this.msg);
console.log("updated-dom: " + document.getElementById("sp").innerText);
},
// ==================== Destruction phase ====================
// 7. The seventh function of the life cycle , When this function executes ,Vue All data in methods componet Not destroyed
beforeDestory() { },
// 8. The eighth function of the life cycle , When this function executes ,Vue The instance is completely destroyed
destoryed() { }
}); </script>

![ Insert picture description here ](https://s2.51cto.com/images/20210808/1628416908531743.jpg)
[](
)Vue Middle component （Component）
=====================================================================================
** Function of components **： To reduce Vue Amount of code in the instance object , Use... In the future Vue Development process , The page can be divided into different components according to different business functions , Then multiple components complete the layout of the whole page , Easy to use in the future Vue Page management during development , Convenient for developers to maintain .
[](
) Development of global components
--------------------------------------------------------------------------
Global components registered with Vue example , It can be done anywhere Vue Use the component within the scope of the instance .
Development of global components ：


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<!-- Use global components -->
<login></login>
<!-- Using local components -->
<user-login></user-login>

// Parameters 1: Component name
// Parameters 2: Component configuration object template: Used to write components html Code ( Be careful : stay template A container must exist in the )
Vue.component('login', {
template : '<div> The user login </div>'
});
// Components of hump nomenclature will be specially treated , userLogin It must be written as user-login
Vue.component('userLogin', {
template : '<div><input type="button" value=" Sign in "></div>'
});
const app = new Vue({
el: "#app",
data: {},
methods: {},
}); </script>

![ Insert picture description here ](https://s2.51cto.com/images/20210808/1628416908113583.jpg)
[](
) Development of local components
--------------------------------------------------------------------------
By registering the component with the corresponding Vue One in the instance `components` Property to complete component registration , This way won't be right Vue Instances cause accumulation .
The first development method ：


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<login></login>
<login></login>
<login></login>

const login = {
template: '<div><h2> The user login </h2></div>'
};
const app = new Vue({
el: "#app",
data: {},
methods: {},
components: { // Local components
login: login // Register local components
}
}); </script>

The second development mode ：


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<login></login>
<login></login>
<login></login>

<h2> The user login </h2>

const login = { // Specific local component name
template: '#loginTemplate' // Definition template Label selector is OK
};
const app = new Vue({
el: "#app",
data: {},
methods: {},
components: { // Local components
login: login // Register local components
}
}); </script>

![ Insert picture description here ](https://s2.51cto.com/images/20210808/1628416908430469.jpg)
[](
) In the component props Use
================================================================================
`props` It is used to transfer corresponding static data or dynamic data to components ;
[](
) Declare static data on the component and pass it to the component
------------------------------------------------------------------------------------


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<!-- Use components , Static data transfer through components -->
<login user-name="zhenyu" age="20"></login>

let login = {
template: '<div><h2> welcome : {{ userName }} Age : {{ age }}</h2></div>',
props: ['userName', 'age'] // props: It is used to receive the data passed through the component tag when using the component
}
const app = new Vue({
el: "#app",
data: {},
methods: {},
components: {
login // Component registration
}
}); </script>

![ Insert picture description here ](https://s2.51cto.com/images/20210808/1628416909341667.jpg)
[](
) Declare dynamic data on the component and pass it to the component
------------------------------------------------------------------------------------


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<!-- Use components to receive Vue Dynamic data in the instance -->
<!-- Use v-bind Form to bind data to Vue In the example data attribute , data Property changes , The internal data of the component changes accordingly -->
<login v-bind:name="username" :age="userage"></login>

 template: '<div><h2> welcome : {{ name }} Age : {{ age }}</h2></div>',
props: ['name', 'age']
}
const app = new Vue({
el: "#app",
data: {
username: "zhenyu",
userage: 25
},
methods: {},
components: {
login // Certified components
}
}); </script>

![ Insert picture description here ](https://s2.51cto.com/images/20210808/1628416909930747.jpg)
[](
)props One way data flow of
-------------------------------------------------------------------------------
be-all props Both make their father and son props There is a ** One way downlink binding **： Parent props The update flows down to the child component , But not the other way around . This prevents accidental changes to the state of the parent component from the child component , This causes your application's data flow to be difficult to understand .
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