Detailed notes of ES6

let

1. A new way to declare variables .
2. Variables cannot be declared repeatedly .
3. Block level scope . in other words let Only in code blocks , Include if、else Variables in curly braces will not be defined to the global .
4. No variable promotion . in other words , Using variables before declaring them will result in an error .
5. Does not affect the scope chain effect . That is to say , Look up variables in functions , Function outside by let Variables defined , You can still find .

use let Achieve loop traversal . This is because it only takes effect in the block level scope .

const

Used to declare a constant , The value cannot be modified .

1. Be sure to assign the initial value .
2. General constants use uppercase （ Hidden rules ）
3. The value of a constant cannot be modified .
4. Block level scope
5. For the element modification of arrays and objects , It does not count as modifying constants , No mistake. .（ Because the address pointed to has not changed ）

Deconstruction and assignment of variables

Extract values from arrays and objects in a certain pattern .

The deconstruction of arrays

Object deconstruction

Template string

` I am also a string ~`

1. Line breaks can appear directly in the content
2. Variable splicing , Use ${}

Simplified writing of objects

The attribute name is the same as the attribute value. You can write only one .

Functions can also be written directly .

Arrow function

1. In the arrow function this Is static , Always point to... Under the scope where the function is declared this value .

2. Cannot be used as a constructive instance object
   

3. Out of commission arguments Variable
   

4. Shorthand for arrow function
   
   

The default value of the function parameter

After passing the parameters, we will use the passed parameters , No arguments passed in , Let's use the default value .


The default value can be used with deconstruction assignment .

You can also pass in the default value .

rest Parameters

rest Must be placed at the end of the parameter . The output is an array .

Extension operator

Symbol

Symbol Brief introduction

Summary of data types ：

utilize Symbol Add properties to the object

When adding attributes to objects, we don't have to worry about naming conflicts .

Symbol Built in values

Control type detection by yourself .

Control whether the value can be expanded .

Extend the functionality of objects ~~

iterator

for of Traversal key value ,for in Traversal key name

generator

Generator is a special function , An asynchronous function , Pure callback functions .
yield It can be regarded as the cutter of function code , Every time you use a function next() To execute the code .

for of What I'm going through is value.

Parameters of generator function

The parameter passed in will be used as the return value of the code executed once .

promise