JavaScript Object-oriented basics (1)

There are 3 common ways to create objects:

① How variables are declared

var function () {Console.log (this. key1)}}var array = [1, 2, 3];

You can continue to add properties and methods to obj1 , such as:

Obj1.color = "Red"function () {console.log ("AAA")};

② using operator new

var New Object ();

You can continue to add properties and methods to Obj2 , such as:

Obj2.name = "Madom"function () {console.log ("AAA")};

③ Creating constructors

function Cat () {             
this. Age = "+";  This function　　() {console.log (this. Age); }}　　

In fact, the constructor is also a normal function, only when the new operation is the constructor,

Creates an instance object from a constructor function. Each object has its own internal prototype proto_

The individual instance objects are not the same.

var New  //truevarnew/ /// Fals  

Then create a constructor with return

function Bird () {    this. Age =N;       This function () {Console.log (' my age is ' +)};     return {        ' Tim ',        functionthis. name},}    ;}

Create an object instance to see what's different

var New  //  Hello Tim//  Object {name: "Tim", say:function}

Discovery: If the constructor has a return, the object instance cannot use the property and method before the constructor return

The internal operation of the new operation is generally as follows:
1th Step: Open a space in memory.
2nd step: Create a new empty object and point this to this empty object.
3rd Step: Point the internal prototype of the empty object to the prototype object of the constructor.
4th step: When the constructor execution is complete, if there is no return (returned value) , Then there is an ' implicit ' return This at the end of the constructor function If there is a return value , thereturn value is assigned to the object instance.

Perform the following simulation of the creation of the instance ( non-Real execution ):

var New Cat (); /* This = {}, * this._proto_ = Cat.prototype * this = CAT1; * Return this  */

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JavaScript Object-oriented basics (1)