TS readonly 只读属性

可以在 interface type 和 类 里使用 readonly 修饰属性

class AbstractExtension<T, U> {
  public readonly type: ExtensionType;
  public readonly manifest: IExtensionManifest;
  public readonly extensionLifeCycle: IExtensionLifeCycle<T, U>;

  constructor(
    type: ExtensionType,
    manifest: IExtensionManifest,
    extensionLifeCycle: IExtensionLifeCycle<T, U>
  ) {
    this.type = type;
    this.manifest = manifest;
    this.extensionLifeCycle = extensionLifeCycle;
  }
}

指定一个类的属性为只读，然后在声明时或者构造函数中初始化它们

class Foo {
  readonly bar = 1; // OK
  readonly baz: string;
  constructor() {
    this.baz = 'hello'; // OK
  }
}