super What is it? ？

： It's just a keyword Usage for super（…） perhaps super.xxx （…）
because super The grammatical definition of and this Different this Is defined as this This keyword will be replaced with a reference
super It is super（…） Will be replaced by a call Except in the constructor It's called directly in super Outside , You can also use super.xxx （…） To call a prototype method on the parent class , It's also a restricted grammar

Say the running results of the following program

(function() {
     
	let a = this ? class b {
    } : class c {
    } ; 
	console.log(typeof a, typeof b , typeof c)
})()

The result is function undefined undefined
When defining function variables , Function names can only take effect in function bodies

How do you understand ES6 in Module Of ? What are the use scenarios ?

Introduce

modular ,（Module）, It is a collection of program statements that can independently name and complete certain functions （ That is, the aggregation of program code and data structure ）.

Two basic features ： External and internal features
External feature refers to the interface between module and external environment （ That is, how other modules or programs call the module , Including input and output parameters 、 Global variables referenced ） And module functions
Internal characteristics refer to the characteristics of the internal environment of a module （ That is, the local data and program code of the module ）

Why modularity is needed
Code abstraction
Code encapsulation
Code reuse
Dependency management

Without modularity , What will happen to our code ？
1) Variables and methods are not easy to maintain , Easy to pollute global scope
2) The way to load resources is through script Label from top to bottom .
3) The subjective logic of the dependent environment focuses on , More code will be more complex .
4) Large project resources are difficult to maintain , Especially when many people work together , The introduction of resources will make people run away

AMD
Asynchronous ModuleDefinition（AMD）, Asynchronous module definition , Load the module asynchronously . All statements that depend on the module , Are defined in a callback function , Wait until the module is loaded , This callback function will run
The representative library is require.js

CommonJs
CommonJS It's a set Javascript The module specification , For the server
It has the following characteristics ：
All code runs in the module scope , Does not contaminate the global scope
Modules are loaded synchronously , That is, only the loading is complete , To perform the following operations
The module is cached after its first execution , Reloading only returns cached results , If you want to execute again , The cache can be cleared
require The returned value is a copy of the output value , Changes within the module will not affect this value

ES6 At the level of language standards , Realized Module, Module function , It can completely replace CommonJS and AMD standard , Become a common module solution for browser and server
CommonJS and AMD modular , They can only be identified at runtime . such as ,CommonJS Modules are objects , You have to look for object properties when you type

Use

Module function is mainly composed of two commands ：
export： It is used to specify the external interface of the module
import： It is used to input the functions provided by other modules
export
A module is a separate file , All variables within the file , External cannot get . If you want the external to be able to read a variable inside the module , Must use export Keyword output the variable
import
Use export After the command defines the external interface of the module , other JS The file can be passed import Command to load this module

Use scenarios

Now ,ES6 Modularity has gone deep into our daily project development , image vue、react Project construction project , Component development can be seen everywhere , It also relies on modular implementation