Question

在nodejs中检查继承的最佳方法是什么？

我试图在继承此模块的类的另一个模块的类的实例中使用instanceof。

档案a.js

    class A{

    }

    class B extends A{

    }

    var b = new B();

    b instanceof A ///this work
    global.c instanceof A //this doesn't work

    module.exports = A;

档案c.js

var A = require("./a");

class C extends A{

}

global.c = new C();

Answer 1

这是因为加载问题！当您加载C类时，它会请求A类，并在定义C之前运行。

我自己尝试过，如果我按照你提到的那样做并要求两个类，第二个比较失败了。

然而这个有效：

a.js

class A{
    callMeLaterAligator(){
        console.log(b instanceof A) ///this work
        console.log(global.c instanceof A) //this now work
    }
}

class B extends A{

}

var b = new B();

module.exports = A;

c.js

var A = require("./a");

class C extends A{

}

global.c = new C();

主要方法

require('services/c');
const a = require('services/a');
const aInst = new a();
aInst.callMeLaterAligator();

有输出

true
true

为了更好地了解最新情况，我创建了这个例子

a.js

console.log('Hello, I am class A and I am not yet defined');
class A{

}

class B extends A{

}

var b = new B();

console.log('Hello, I am class A and I will compare something');
console.log(b instanceof A) ///this work
console.log(global.c instanceof A) //this doesn't work

module.exports = A;

c.js

console.log('Hello, I am class C and I am not yet defined');

var A = require("./a");

console.log('Hello, I am class C and I will now try to defined myself');

class C extends A{

}

console.log('Hello, I am class C and I am defined');
global.c = new C();

console.log('Hello, I am class C and I am in global.c');

server.js

require('services/c');

有了这个输出

Hello, I am class C and I am not yet defined
Hello, I am class A and I am not yet defined
Hello, I am class A and I will compare something
true
false
Hello, I am class C and I will now try to defined myself
Hello, I am class C and I am defined
Hello, I am class C and I am in global.c

如果您将其更改为要求＆＃34; a＆＃34;首先，然后C根本没有加载

server.js更改：

require('services/a');

有了这个输出

Hello, I am class A and I am not yet defined
Hello, I am class A and I will compare something
true
false

检查nodejs中的继承

1 个答案: