何时以及如何将装饰器应用于@angular包中的装饰类

Question

如果我在我的类中使用装饰器,则在导入类时会评估装饰器.这是一个小例子:

@NgModule({ ... })
export class BModule { ... }

透露为:

var BModule = (function () {
    function BModule() {
    }
    BModule = __decorate([  <---------- decorators are applied here
        core_1.NgModule({...})
    ], BModule);
    return BModule;
}());
exports.BModule = BModule;

但是,当在@angular包中应用模块或任何其他装饰器时,输出如下:

var HttpClientModule = (function () {
    function HttpClientModule() {
    }
    return HttpClientModule;
}());
HttpClientModule.decorators = [
    { type: _angular_core.NgModule, args: [{ ... },] },
];

如您所见,装饰器不适用于此处.他们只是保存在decorators酒店.为什么它与我的代码不同？

我问的原因是,在导入我的装饰类时,我希望它应用了装饰器,因此可以使用Reflect:

const providers = Reflect.getOwnMetadata('annotations', BModule);

但是,对于@angular包中的装饰类,它不能以这种方式工作.

Answer 1

当angulat解析注释时,它有三个选项:

1)直接API

// Prefer the direct API.
if ((<any>typeOrFunc).annotations && (<any>typeOrFunc).annotations !== parentCtor.annotations) {
  let annotations = (<any>typeOrFunc).annotations;
  if (typeof annotations === 'function' && annotations.annotations) {
    annotations = annotations.annotations;
  }
  return annotations;
}

我们通常在ES5中编写代码时使用此API

MyComponent.annotations = [
  new ng.Component({...})
]

2)tsickle的API

// API of tsickle for lowering decorators to properties on the class.
if ((<any>typeOrFunc).decorators && (<any>typeOrFunc).decorators !== parentCtor.decorators) {
  return convertTsickleDecoratorIntoMetadata((<any>typeOrFunc).decorators);
}

这种方式角度从@angular/(core|material...)库中读取注释.Angular以这种方式编译库,因为它有助于优化bundle.例如,我们不需要像装饰器那样运送装饰器_decorate, __metadata,代码将更快地执行.

tslib通过运行带有--importHelpers选项https://github.com/angular/angular/blob/master/build.sh#L127的 tsc来构建库时的角度用途.

Angular材料做同样的事情https://github.com/angular/material2/blob/master/tools/package-tools/rollup-helpers.ts#L9-L11

// Import tslib rather than having TypeScript output its helpers multiple times.
// See https://github.com/Microsoft/tslib
'tslib': 'tslib',

3)使用反射

// API for metadata created by invoking the decorators.
if (this._reflect && this._reflect.getOwnMetadata) {
  return this._reflect.getOwnMetadata('annotations', typeOrFunc);
}

当我们使用typescript发出的元数据时使用此API

为确保您能正确获取元数据,您可以考虑使用以下函数:

declare let Reflect: any;
function getAnnotations(typeOrFunc: Type<any>): any[]|null {
  // Prefer the direct API.
  if ((<any>typeOrFunc).annotations) {
    let annotations = (<any>typeOrFunc).annotations;
    if (typeof annotations === 'function' && annotations.annotations) {
      annotations = annotations.annotations;
    }
    return annotations;
  }

  // API of tsickle for lowering decorators to properties on the class.
  if ((<any>typeOrFunc).decorators) {
    return convertTsickleDecoratorIntoMetadata((<any>typeOrFunc).decorators);
  }

  // API for metadata created by invoking the decorators.
  if (Reflect && Reflect.getOwnMetadata) {
    return Reflect.getOwnMetadata('annotations', typeOrFunc);
  }
  return null;
}

function convertTsickleDecoratorIntoMetadata(decoratorInvocations: any[]): any[] {
  if (!decoratorInvocations) {
    return [];
  }
  return decoratorInvocations.map(decoratorInvocation => {
    const decoratorType = decoratorInvocation.type;
    const annotationCls = decoratorType.annotationCls;
    const annotationArgs = decoratorInvocation.args ? decoratorInvocation.args : [];
    return new annotationCls(...annotationArgs);
  });
}


const annotations = getAnnotations(AppModule);

更新:

通过调用装饰器创建的元数据的API在5.0.0-beta.4中已更改

const ANNOTATIONS = '__annotations__';

// API for metadata created by invoking the decorators.

if (typeOrFunc.hasOwnProperty(ANNOTATIONS)) {
   return (typeOrFunc as any)[ANNOTATIONS];
}
return null;