为什么Angular10会出现“Cannot set properties of undefined...”的错误？

Question

我正在开发一个用户可以注册的应用程序，为此用户必须写入姓名、昵称、密码、身份证明类型等数据...

用户型号：

export class User{
    id: string;
    name: string;
    nickname: string;
    password: string;
    docType: {
        documentTypeId: number;
    }
}

组件.ts:

public insertUser(event: Event): void{
      event.preventDefault();
        
      const u: User = new User();

      u.id = this.form.value.id;
      u.name = this.form.value.name;
      u.nickname = this.form.value.nickname;
      u.password = this.form.value.password;
      u.docType.documentTypeId = Number(this.form.value.typeId); // the error occurs here

      /*send to API, save to DB... */ 
}

所以，u.docType.documentTypeId的值赋值时出现错误，我不知道我做错了什么。

Answer 1

这个有用吗：

u.docType = {
    documentTypeId: Number(this.form.value.typeId);
}

我认为应该！

为什么Angular10会出现“Cannot set properties of undefined...”的错误？

Why the error " Cannot set properties of undefined..." appears in Angular 10?

exception

angular-material

angular