newechoes/src/content/理解计算机/Web/Javascript/SE6.md

title	date	tags
SE6	2024-09-19T10:31:39Z

object

closure

closure=inner function+external function variable

function f1() {
    let i=0
    function f2() {
        i++
        console.log(i)
    }
    return f2
}
const f=f1()

construct object

function Pig(name,age,gender){
    this.name = name
    this.age = age
    this.gender = gender
    }
const pappe = new Pig('佩奇',6,'女')

Instance members: methods and properties on property objects

Static members: static properties and methods

convention

1. can only start with a capital letter
2. can only be executed using the 'new' operator

prototype

function Pig(name,age){
    this.name = name
    this.age = age
    }
Pig.prototype.sing=function(){}
const pappe = new Pig('佩奇',6)

1. each cpmstructor has a prototype property
2. This object mounting function will not create functions on the prototype multiple times during object instantiation, saving memory

constructor

1. Refers back to the constructor created

object prototype

​__proto__​ =[[proto]]​

inherit

function Person(){
        this.gender=1
}
function A(uname,age){
       this.uname = uname;
       this.age = age;
}
A.prototype=new Person()
A.prototype.constructor=A

Prototype Chain

Inheritance based on prototype objects associates different constructor objects together

instanceof

You can use instanceof​ to check if the prototype property of the constructor appears on the prototype chain of an instance object

function

parmeter

• dynamics parmeter

  arguments
  

  The paseudo array includes all the parameters passed in

• remaining parameters

  function f(...<parameter name>){
      <parameter name> //array
  }
  

Arrow function

const <function name> = () =>{}

rule

1. If the function has only one line, it can be written on one line, {} can be omitted, and there is no need to write a return to have a return value. If the return dictionary needs to be written, () needs to be added
2. if there is only parameter,()can beomitted

this

the arrow function does not have this,it wil only use this from the higer-level scope chain

deconstruction

{name:newname,age:newage}={name:lsy;age:19}

1. The variable names for deconstruction need to be consistent with those in the object
2. Rename: The previous name is the opposite name, followed by the new name that needs to be changed. If not changed, do not use write

multistage

obj={
    a:1
    b:{
        b1:2
        b2:3
        }
    c:4
}
{a,b:{b1,b2},c}=obj

array

Expand operator

...<array>

deconstruction array

[a,b]=[1,2]

1. Assign the variables on the left to the variables on the right in sequence
2. Support multidimensional arrays

copy

shallow copy

If it is a complex data type, only copy the address

1. object

   Object.assign(<new>,<old>)
   

2. array

   Array.prototype.concat()
   

deep copy

1. recursion
2. json
3. Library functions

performance optimization

	explain
debounce	Frequent triggering of events within a unit time, only executing the last time
throttle	Frequent triggering of events per unit time, only executed once