TypeScript - 如何继承类并覆盖lambda方法 [英] TypeScript - how to inherit class and override lambda method

问题描述

我有一个继承的类，并且需要父类具有一个虚方法，该方法在子类中被重写。这个方法是从基础构造函数调用的，需要访问实例属性，所以它需要是一个lambda函数，所以this就是_this。问题是，覆盖lambda方法对我来说不起作用，就像重写非lambda一样。这可能吗？如果没有，我想了解原因。

I have an inherited class, and need the parent to have a virtual method, which is overridden in the child class. This method is called from the base constructor, and needs access to instance properties, so it needs to be a lambda function, so "this" is "_this". The problem is, overriding a lambda method does not work for me like overriding a non-lambda does. Is this possible? If not, I'd like to understand why.

此外，当仅从构造函数调用方法时，this是否始终与_this相同？

Also, will "this" always be the same as "_this" when the method is only called from the constructor?

class Base {
    protected prop = null;
    constructor() {
        this.init();
        this.initLambda();
    }
    init() {
        console.log("Base init");
    }
    initLambda = () => {
        console.log("Base initLambda");
    }
}
class Derived extends Base {
    constructor() {
        super();
    }
    init() {
        console.log("Derived init");
    }
    initLambda = () => {
        //let x = this.prop;
        console.log("Derived initLambda");
    }
}

输出：

派生初始化

基础initLambda

Output:
Derived init
Base initLambda

推荐答案

好吧，你不能拥有它。

有已打开的问题，但已按按设计关闭。

Well, you can't have that.
There's an issue that was opened but it was closed as "by design".

你应该使用常规方法：

class Base {
    protected prop = null;

    constructor() {
        this.init();
        this.initLambda();
    }

    init() {
        console.log("Base init");
    }

    initLambda() {
        console.log("Base initLambda");
    }
}

class Derived extends Base {
    constructor() {
        super();
    }

    init() {
        console.log("Derived init");
    }

    initLambda() {
        console.log("Derived initLambda");
    }
}

然后它会起作用。

至于保持正确这个，你总是可以像箭头函数那样调用方法：

As for keeping the right this, you can always pass a call to the method as an arrow function:

doit() {
    setTimeout(() => this.init(), 1);
}

或者使用 Function.prototype.bind 功能：

setTimeout(this.init.bind(this));

此外，打字稿的 _this 编译器生成只是对ES5的箭头函数进行polyfil的黑客攻击，但是如果你将目标更改为ES6则它将不会使用它。

Also, the _this thing that the typescript compiler produces is just a hack to polyfil the arrow functions for ES5, but if you change the target to ES6 then it won't use it.

您可以将绑定方法保存为成员：

You can save the bound methods as members:

class Base {
    ...
    public boundInit: () => void;

    constructor() {
        ...
        this.boundInit = this.initLambda.bind(this);
        setTimeout(this.boundInit, 500);
    }

...

有了这个，当我做 new Derived（）这就是我得到的：

With that, when I do new Derived() this is what I get:

派生的init

派生的initLambda //在200毫秒之后

Derived init
Derived initLambda // after 200 millis

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