javascript - Object.keys(myObject) 不返回 typescript 中类的属性

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

除非您初始化这些属性，否则它们实际上不会被创建。您可以查看转发的Provider.js归档并验证。这只是告诉编译器，每当我们在 Provider 实例中使用它时的一种方式。 ，强制使用这些预定义类型。

在 Typescript Playground 上测试它

该类:

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在转译的构造函数中创建为属性。