在Typescript中如何修复无法设置未定义的属性“first” [英] In Typescript how to fix Cannot set property 'first' of undefined

问题描述

我正在尝试设置 Name 界面中定义的子属性 first 但是什么时候所以我总是得到一个错误，例如：

I'm trying to set a the sub property first that is defined in the Name interface but when do so I always get an error for example:

interface Name{
    first: string,
    last:string,
}

class Person{

    private name:Name

    public setName(firstName, lastName){
        this.name.first = firstName;
        this.name.last = lastName;
    }

}


var person1  = new Person();
person1.setName('Tracy','Herrera');

运行时我收到错误：无法设置'first'的属性undefined

任何人都有想法解决这个问题吗？

Any one have an idea to work this out?

推荐答案

在实例化时不会自动初始化类属性。您需要手动使用相应的对象初始化它们 - 在这种情况下，使用包含其接口定义的属性的对象：

Class properties are not automatically initialized on instantiation. You need to initialize them with the corresponding objects manually -- in this case, with an object containing the properties defined by its interface:

class Person {
    private name: Name;

    public setName(firstName, lastName) {
        this.name = {
            first: firstName,
            last: lastName
        };
    }
}

---

另一种方法 - 例如，如果有多个方法在同一个对象上设置属性 - 首先将属性初始化为空对象，最好是在构造函数中：

---

Another approach -- for example, in case there are multiple methods setting properties on the same object -- is to first initialize the property to an empty object, preferably in the constructor:

class Person {
    private name: Name;

    constructor() {
        this.name = {};
    }

    public setName(firstName, lastName) {
        this.name.first = firstName;
        this.name.last = lastName;
    }

    public setFirstName(firstName) {
        this.name.first = firstName;
    }
}

但是，使用当前设置，这将产生一个编译将 {} 分配给 this.name 时出错，因为名称 interface 要求在对象上存在第一个和 last 属性。要克服此错误，可以使用在接口上定义可选属性：

However, with the current setup this will yield a compile error when assigning {} to this.name, because the Name interface requires the presence of a first and a last property on the object. To overcome this error, one might resort to defining optional properties on an interface:

interface Name {
    first?: string;
    last?: string;
}

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