检查typescript类是否有setter / getter [英] Check if typescript class has setter/getter

问题描述

我有一个打字稿类，它具有以下属性：

I have a typescript class which has the following properties:

export class apiAccount  {
    private _balance : apiMoney;
    get balance():apiMoney {
        return this._balance;
    }
    set balance(value : apiMoney) {
        this._balance = value;
    }

    private _currency : string;
    get currency():string {
        return this._currency;
    }
    set currency(value : string) {
        this._currency = value;
    }
    ...

我需要创建一个这样的空白实例class：

I need to create a blank instance of this class:

let newObj = new apiAccount();

然后检查它是否具有货币的设置者。
我认为这正是 getOwnPropertyDescriptor 的确如此，但显然我错了：

And then check if it has the setter for "currency", for example. I thought that this is exactly what getOwnPropertyDescriptor does, however apparently I was wrong:

Object.getOwnPropertyDescriptor(newObj, 'currency')
Object.getOwnPropertyDescriptor(newObj, '_currency')

这两个都返回undefined。但铬似乎做到了！当我将鼠标悬停在实例上时，它会向我显示属性，并将它们显示为未定义。如何获取这些属性名称的列表，或检查对象中是否存在属性描述符？

These both return undefined. But chrome seems to do it! When I hover over the instance, it shows me the properties, and shows them as undefined. How can I get a list of those property names, or check if the property descriptor exists in the object?

推荐答案

问题是 Object.getOwnPropertyDescriptor - 顾名思义 - 只返回对象自己的属性的描述符。即：只有直接分配给该对象的属性，不来自其原型链中某个对象的属性。

The "problem" is that Object.getOwnPropertyDescriptor - as the name implies - only returns descriptors of an object's own properties. That is: only properties that are directly assigned to that object, not those that are from one of the objects in its prototype chain.

In例如，货币属性是在 apiAccount.prototype 上定义的，而不是在 newObj上定义。以下代码段演示了这一点：

In your example, the currency property is defined on apiAccount.prototype, not on newObj. The following code snippet demonstrates this:

class apiAccount {
    private _currency : string;
    get currency():string {
        return this._currency;
    }
    set currency(value : string) {
        this._currency = value;
    }
}

let newObj = new apiAccount();
console.log(Object.getOwnPropertyDescriptor(newObj, 'currency')); // undefined
console.log(Object.getOwnPropertyDescriptor(apiAccount.prototype, 'currency')); // { get, set, ... }

如果你想在任何地方找到一个属性描述符一个对象的原型链，你需要循环 Object.getPrototypeOf ：

If you want to find a property descriptor anywhere in an object's prototype chain, you'll need to loop with Object.getPrototypeOf:

function getPropertyDescriptor(obj: any, prop: string) : PropertyDescriptor {
    let desc;
    do {
        desc = Object.getOwnPropertyDescriptor(obj, prop);
    } while (!desc && (obj = Object.getPrototypeOf(obj)));
    return desc;
}

console.log(getPropertyDescriptor(newObj, 'currency')); // { get, set, ... }

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