Object.keys(myObject) 不会在打字稿中返回类的属性

Question

为什么：

let provider = new Provider();
var keys = Object.keys(provider);
console.log(keys);

返回一个空数组，当：

let provider = { Name: '', Surname: '' };
var keys = Object.keys(provider);
console.log(keys);

返回一个包含 2 个属性的数组？

这是我的Provider.ts ：

export class Provider {
  public Id: string;
  public Name: string;
  public FriendlyName: string;
  public CompanyRegistrationNumber: string;
  public VatRegistrationNumber: string;
  public TfgUniqueReferenceNumber: string;
  public Since: Date;
  public Until: Date;
  public DefaultBillingDay: number;
  public DefaultProvisioningDay: number;
  public AllowsToProvisionProRata: boolean;
  public AllowsToBillProRata: boolean;
  public EmailAddress: string;
  public DateCreated: Date;
  public DateModified: Date;
  public UserCreated: string;
  public UserModified: string;
  public IsRetired: boolean;
  public ImageUrl: string;
  public ContactNumber1: ContactNumber;
  public ContactNumber2: ContactNumber;
  public PhysicalAddress: Address;
  public PostalAddress: Address;
  public FinancialSystemAccount: FinancialSystemAccount;
  public WholesaleProducts: Array<WholesaleProduct>;
  public ContactPeople: Array<ContactPerson>;
  public Batches: Array<Batch>;
  public BatchCandidates: Array<BatchCandidate>;
  public AllowableBatchTypes: Array<BatchType>;
}

Answer 1

除非您初始化属性，否则实际上不会创建它们。 您可以检查 trasnpiled Provider.js文件并验证它。 这只是告诉编译器的一种方式，每当我们在Provider的实例中使用它时，就强制使用那些预定义的类型。

在Typescript Playground上测试

这节课：

class Provider {
  public Id: string;
  public Name: string;
  public FriendlyName: string;
  public CompanyRegistrationNumber: string;
  public VatRegistrationNumber: string;
  public TfgUniqueReferenceNumber: string;
  public InitializedProp: string = '';
}

被转译为：

var Provider = (function () {
    function Provider() {
        this.InitializedProp = '';
    }
    return Provider;
}());

您可以看到只有InitializedProp被创建为转译的构造函数中的属性。