Detailed explanation of code examples of inheritance mechanism in Javascript

JavaScriptInheritanceIn many books, many types and implementation methods are carefully divided into many types and implementation methods. There are generally two types:ObjectImpersonation and prototype methods . These two methods have their own advantages and disadvantages. I will list them here first, and then analyze the differences from the bottom level

After learning the creation of Javascript classes and objects, now I will summarize the implementation of the Javascript inheritance mechanism. Javascript does not have a strict and clear definition of the inheritance mechanism like Java. Its implementation is very loose just like the use of itsvariables. You can design your own method to "imitate" the inheritance mechanism. accomplish. There are several methods:

1. Object impersonation

The code block defined by function is equivalent to a class, you can use it and it has this keyword, you can use this for it Add attributes and methods. There are the following two sentences in the above code:

this.newMethod1=classA; this.newMethod1(str);

The newMethod1 variable is defined in classB, which is areference, pointing to classA, and also calling classA. These two The function of the sentence code is equivalent to directly copying the content in the classA code block here. The classB object created in this way will of course have the attributes and methods of classA. Object impersonation can also achieve multiple inheritance, as follows:

function ClassZ() { this.newMethod = ClassX; this.newMethod(); delete this.newMethod; this.newMethod = ClassY; this.newMethod(); delete this.newMethod; }

However, classY will override the properties and methods of the same name in classX. If there is no problem with the design, classz should not inherit different classes with the same properties and methods.

2. Use the call() method

to pass an object as the first parameter in the call() method. This here refers to the current object, and the following Parameters (there may be multiple) refer to the parameters required to be passed to the class (function) that calls the call() method. classA.call() is also equivalent to directly copying the content in the classA code block. At this point, objects of classB can also directly use variables and methods in classB.

3. Prototype chain

The prototype keyword is used to define the class here. There are no parameters when defining the function. The variables or methods after prototype are equivalent to the ones in java.staticThe modified properties and methods belong to all objects. There is a special feature here: cB.prototype=new cA(); This sentence is equivalent to copying the content of the cA object to cB, and cB can also be appended own properties and methods.

4. Mixed method

Here you can encapsulate the attributes in the class body, and use the prototype method to define the method. Personally, this is a good design method, using functions defined by prototype. It can be reused for multiple objects. Two points need to be noted here: there is cA.call(this,name) in the cB class body; at the same time, the cB prototype must be assigned to the cB object, that is: cB.prototype=new cA();cA. call(this,name) is also equivalent to copying the code in the cA class block here. The following sentence adds the methods of cA to cB. At the same time, cB can also add its own properties and methods.

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