Javascript中的虚函数 [英] Virtual function in Javascript

问题描述

我在问如何在C#之类的javascript中实现虚拟功能

I am asking how to implement the virtual function in the javascript like C#, let's say

• 我有一个基类A
• 我还有一个名为B的派生类
• 类A有一个名为virtualFunction的函数，应该像在C#中那样是一个虚函数，可以在派生类B中覆盖它.
• 该函数将被调用以在基类A的构造函数中执行.如果该函数在B中被覆盖，则将调用B的函数，否则将调用A的函数

在下面的示例中，我想获得"B"警报，而不是"A"警报.

With this example below, I want to get a 'B' alert, not the 'A'.

function A() {
  this.virtualFunction();
}

A.prototype.virtualFunction = function() {
  alert('A');
};

//-------------------------------------

function B() {}

B.prototype = new A();
B.prototype.virtualFunction = function() {
  alert('B');
};

var b = new B();

如果我们在实例化之后调用函数，就像这样，那没关系，但我需要在构造函数内部"

If we invoke the function after instanced, like this, then it is okay, but I need "inside the constructor"

var b = new B();
b.virtualFunction();

推荐答案

因此，首先要意识到的是JavaScript与C#使用的语义不同.试图这样做会导致您心痛；学习JS中的事情是更好的选择.实际上，大多数人并没有尝试在JS中做很多继承类型的事情，而是偏爱组合(这实际上是我所熟悉的所有OO语言中的最佳实践).

So, the first thing to realize is that JavaScript doesn't use the same semantics as C#. Trying to get it to do so will cause you heartache; you're much better off learning how things are done in JS. In fact, most folks don't try to do a lot of inheritance type stuff in JS, but instead favor composition (which is actually a best practice in all OO languages I'm familiar with).

也就是说，您可以对代码进行一些改进.

That said, there's a few improvements you could make to your code.

function A() {
  this.virtualFunction();
}

A.prototype.virtualFunction = function() {
  alert('A');
};

//-------------------------------------

function B() {
   A.call(this);
}

B.prototype = Object.create(A.prototype);
B.prototype.constructor = B;
B.prototype.virtualFunction = function() {
  alert('B');
};

var b = new B();

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