Daily notes~

vite

 Create a project 
npm init vite-app  Project name 
 Enter the project directory 
cd  Project name 
 Installation dependency 
npm install
 function 
npm run dev

setup

 understand  vue3.0 A new configuration item in , Value is a function 
setup It's all Composition API( Combine API) The performance stage 
 Components used in   data   Methods, etc.   All shall be configured in setup in 
setup Two return values of function 
     If you return an object   Then the properties in the object   Methods can be used directly in templates  ( Focus on )
     If you return a rendering function   You can customize the rendering content 
 Be careful 
     Try not to contact vue2.x Configuration mix 
    vue2.x To configure (data,methods,computed..) You can access setup Properties in   Method 
     But in setup Cannot access vue2.x To configure (data,methods,computed...)
     If there are duplicate names  setup first 
setup It can't be a async function   Because the return value is no longer return The object of   It is promise  The template can't see return Properties in objects 

ref function

 effect   Define a responsive data 
 grammar  const xxx=ref(initValue)
     Create a reference object containing responsive data (reference object   abbreviation ref object )
    js Operation data in  xxx.value
     Read data from the template   Unwanted .value  direct <div>{
   {xxx}}</div>
 remarks 
     The accepted data can be   Basic types   It can also be object type 
     Basic types of data   Responsiveness still depends on object.defineProperty() Of get and set Accomplished 
     Object type data   Internal help Vue3.0 A new function in --reactive function 

reactive function

 effect   Define the responsive data of an object type ( Basic type don't use it   Use ref function )
 grammar  const  Proxy object =reactive( Source object ) Receive an object ( Or an array ), Returns a proxy object (proxy Instance object of   abbreviation proxy object )
reactive The defined responsive data is deep-seated 
 Give... Internally ES6 Of Proxy Realization   Operate the internal data of the source object through the proxy object 

vue3 The principle of response in

 Realization principle 
     object type   adopt object.defineProperty() Reading properties , Modify to intercept ( The data was hijacked )
     An array type   Intercept by rewriting a series of methods to update the array ( The change method of the array is wrapped )
    Object,defineProperty(data,'count',{
        get(){}
        set(){}
    })
     Existing problems 
         New properties , Delete attribute   The interface doesn't update 
         Modify the array directly by subscript , The interface doesn't update automatically 

vue3 The principle of response

 Realization principle 
     adopt Proxy( agent ) Intercepts any attribute changes in the object   Include   Read and write property values   Attribute addition   Deletion of attributes, etc 
     adopt Reflect( Reflection ) Operate on the properties of the source object 
 let person = {
        name: "zs",
        age: 19,
      };
      //    simulation vue3 Implement responsive in 
      const p = new Proxy(person, {
        //  Someone read p Called when a property of 
        get(target, propName) {
          console.log(target, propName);
          //   return target[propName];
          return Reflect.get(target, propName);
        },
        //  Someone modified it p A property of , Or to p Called when a property is appended 
        set(target, propName, value) {
          //   target[propName] = value;
          Reflect.set(target, propName, value);
        },
        //  Someone deleted p When a property of 
        deleteProperty(target, propName) {
          //   return delete target[propName];
          return Reflect.defineProperty(target, propName);
        },
      });

reactive contrast ref

 Compare... From the perspective of defining data 
    ref Used to define   Basic types of data 
    reactive Used to define   object ( Or an array ) Type data 
     remarks  ref It can also be used to define object or array type data   It will automatically pass through reactive Turn to proxy object 
 Compare... In principle 
    ref adopt object.defineProperty() Of get and set To achieve responsive ( The data was hijacked )
    reactive By using Proxy To achieve responsive ( The data was hijacked ), And pass Reflect Operate the data inside the metadata 
 Compare... From the perspective of use 
    ref Defined data   Operational data needs .value  When reading data, you do not need to read directly from the template .value
    reactive Defined data    Operating data and reading data   No need to .value

setup Two things to pay attention to

setup Actual execution 
     stay beforeCreate Once before ,this yes undefined
setup Parameters of 
    props  Value as object   contain   Passed from outside the component   And the internal declaration of the component has accepted the attribute 
    context  Context object 
        attrs  Value as object   contain   Passed from outside the component   But not in props Properties declared in the configuration   amount to this.$attrs
        slots  Received slot contents   amount to this.$slots
        emit  Distribute functions that automatically take events   amount to this.$emit