Advanced JS related knowledge

Inheritance: Others have properties and methods that the current object does not have, and use them for your own use, which is inheritance

1 Mixed inheritance

var I={ };    
var obj = {
                name: 'jack',
                age:18,
                sayGoodbye : function () {
                                        console.log("goodbye") ;
                }
    }// 混入式继承， a中 将继承obj的所有属性
    for (var k in obj ) {
        a[k] = obj [k] ;
    }

2. Prototype inheritance

1. Using the feature that members in the prototype can be shared by their related objects, inheritance can be realized

2. Implementation steps

a) Adding new members to the prototype object (through the dynamic characteristics of the object) is not inheritance in the strict sense,,,, the instance object inherits the prototype

b) Directly replace the prototype object

1. 
   

1. #Constructor.prototypr = new object

2. The instance object inherits the prototype (new object)

3. If the object originally has properties and methods, using the replacement method will overwrite the original properties and methods

c) Use the mixing method to add members to the prototype object

1. 
   

1. Mix in, traverse the properties and methods of an object, and assign values ​​to another object for...in...

3 .Classic inheritance

js

var object 1 = Object.creat(object 2) ;

At this time, the created object 1 inherits from object 2

Object.creat method has compatibility issues

Solutions: ​ ​ ​2. Customize the function and determine whether the browser supports the Object.create method inside the function. If it does not support it, manually create the object and return it. Otherwise, call it directly

function creat(obj) {    
    if (object.creat){            
    return Object.creat(obj);
       }else{
            function F(){
                }
            F.prototype = obj;            
            return new F();
            }
    }

How to extend built-in objects more safely

function MyArray() {    
this.name = "我是数组"     
}
var arr = new Array();
MyArray.prototype =arr ; // 继承后，我的数组中 就有了原生数组对象的所有属性和方法
var  myArr = new MyArray() ;   // myArr 这个对象就继承自arr

Prototype chain

What is the prototype chain

Each constructor has a prototype object , each object has a constructor, and the prototype object of each constructor is an object, which also has a constructor

Then a chain structure is formed, which we call the prototype chain

Prototype What is inheritance?
By modifying the structure of the prototype chain, the way to achieve inheritance is prototype inheritance

Attribute search principle

When accessing a member of an object, first Check to see if there is one. If there is, use

1. . If not found, go to the prototype object of the current object to find it. If there is, use

2. directly.

   If not found, go to the prototype object of the prototype object to find it. If there is one, directly use

3. to guide the Object. If it is still not found, return null

4. Inheritance achieved by modifying the prototype chain inheritance structure is called prototypal inheritance

function Person() { } ;var p = new Person() ;

p object The objects included are: members of Person.prototype and members owned by itself

Members of Person.prototype are: members of Object.prototype and members of itself

Members of Object.prototype ：

Constructor: Points to the constructor related to the prototype

HasOwnProperty method: Determines whether the exclusive itself has a certain property

properIsEnumerable method: 1. Determines whether the property belongs to The object itself, 2. Determine whether the attribute can be traversed

toString toLocalString: Convert the object into a string The local setting mode applied when toLocalString is converted into a string

ValueOf method: Participate in the object During operation, first call the valueOf method to obtain the value of the object. If the value cannot participate in the operation, the toString method will be called

Function

3 ways to create a function:

Direct declaration

Function expression

new Function()

Function can be used to create functions:

Syntax:

##

 函数名 =  Function ( ) ;  函数名 =  Function();  函数名 =  Function(,,,...

var distinct = new Function(`
            　　var arr = [];
            　　for (var i = 0; i < arguments.length; i++) {
                　　　　if(arr.indexOf(arguments[i])==-1){
                    　　　　arr.push(arguments[i]);
                　　　　}
            　　}
            　　return arr;
        `);

//可以使用Ese下边的符号 来连接字符串进行换行操作 但是存在兼容性问题

console.log(distinct(1, 2, 34, 34, 5, 5));

eval

can convert a string into js code and execute it

Note: When using eval to parse a JSON format string, please note that {} will be parsed into a code segment

1. You can use JSON format characters Splice "var variable name=" eval("var variable name=" + string in JSON format);

2. You can splice ()# before and after the string in JSON format.

##eval("("+JSON format string+")")

Static members and instance members
Static members Properties accessed through the constructor and methods are static members

Instance members
The properties and methods accessed through objects (instances) are instance members

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