Summary of 4 ways to implement inheritance in JavaScript_javascript skills

Although JavaScript does not provide the inheritance keyword, we can still come up with some good ways to implement it.

1. Prototype chain inheritance:

Copy code The code is as follows:

var Base = function()
{
This.level = 1;
This.name = "base";
This.toString = function(){
           return "base";                                    };
};
Base.CONSTANT = "constant";

var Sub = function()
{
};
Sub.prototype = new Base();
Sub.prototype.name = "sub";

Advantages: Judging from the instanceof keyword, an instance is both an instance of the parent class and an instance of the subclass. It seems to be the purest inheritance.

Disadvantages: The attributes and methods of the subclass that are different from the parent class must be executed separately after statements such as Sub.prototype = new Base(); and cannot be packaged in the Sub constructor. For example: Sub.prototype.name = "sub"; multiple inheritance cannot be implemented.

2. Construction inheritance:

Copy code The code is as follows:

var Base = function()
{
This.level = 1;
This.name = "base";
This.toString = function(){
           return "base";                                    };
};
Base.CONSTANT = "constant";

var Sub = function()
{
Base.call(this);
This.name = "sub";
};

Advantages: Multiple inheritance can be achieved, and property settings unique to subclasses can be placed inside the constructor.

Disadvantage: Use instanceof to find that the object is not an instance of the parent class.

3. Instance inheritance:

Copy code The code is as follows:

var Base = function()

{
This.level = 1;
This.name = "base";
This.toString = function(){
           return "base";                                    };
};
Base.CONSTANT = "constant";

var Sub = function()
{
var instance = new Base();
Instance.name = "sub";
Return instance;
};



Advantages: It is an object of the parent class, and the same effect can be obtained by using new to construct the object or not using new to construct the object.

Disadvantages: The generated object is essentially an instance of the parent class, not an object of the subclass; multiple inheritance is not supported.

4. Copy inheritance:

Copy code The code is as follows: var Base = function()

{

This.level = 1;
This.name = "base";
This.toString = function(){
           return "base";                                    };
};
Base.CONSTANT = "constant";

var Sub = function()
{
var base = new Base();
for(var i in base)
         Sub.prototype[i] = base[i];
Sub.prototype["name"] = "sub";
};

Advantages: Supports multiple inheritance.

Disadvantages: low efficiency; unable to obtain non-enumerable methods of the parent class.

These forms have their own characteristics. As far as the code I provide is concerned, it satisfies the following table:

2012-1-10: Supplement, if we don’t need class inheritance, but only object inheritance, for browsers that support ECMAScript 5, we can also use the Object.create method:

Copy code The code is as follows:

var Base = function()
{
This.level = 1;
This.name = "base";
This.toString = function(){
           return "base";                                    };
};
Base.CONSTANT = "constant";

var sub = Object.create(new Base());
sub.name = "sub";