什么是Reflect metadata

其他 C#、Java、Pythone 语言已经有的高级功能，我 JS 也应该要有（诸如C＃和 Java 之类的语言支持将元数据添加到类型的属性或注释，以及用于读取元数据的反射API，而目前 JS 缺少这种能力）
许多用例（组合/依赖注入，运行时类型断言，反射/镜像，测试）都希望能够以一致的方式向类中添加其他元数据。
为了使各种工具和库能够推理出元数据，需要一种标准一致的方法；
元数据不仅可以用在对象上，也可以通过相关捕获器用在 Proxy 上
对开发人员来说，定义新的元数据生成装饰器应该简洁易用；

TS配置

1{
2  "compilerOptions": {
3    "experimentalDecorators": true,
4    "emitDecoratorMetadata": true
5  }
6}

安装reflect-metadata

npm install reflect-metadata

示例

依赖注入 DI

1import 'reflect-metadata';
2
3interface Constructor<T=any> {
4  new (...args: any[]): T;
5}
6
7const Injectable = (): ClassDecorator => () => {
8  //
9};
10
11@Injectable()
12class OtherService {
13  public method() {
14    return 'this is other service';
15  }
16}
17
18@Injectable()
19class AbilityService {
20  constructor(
21    private other: OtherService,
22  ) {}
23  public speak() {
24    return `${this.other.method()} and 汪汪汪`;
25  }
26}
27
28@Injectable()
29class DogService {
30  constructor(
31    private abilities: AbilityService,
32  ) {}
33  public speak() {
34    return this.abilities.speak();
35  }
36}
37
38export { DogService };
39
40export function factory<T>(target: Constructor<T>): T {
41  const providers = Reflect.getMetadata('design:paramtypes', target) || [];
42  const args = providers.map((provider: Constructor) => factory(provider));
43  return new target(...args);
44}

const dog = factory(DogService);
dog.speak();

output：this is other service and 汪汪汪

Controller 控制器

1import 'reflect-metadata';
2
3interface Constructor<T=any> {
4  new (...args: any[]): T;
5}
6
7const PATH_MATA = 'path';
8const METHOD_MATA = 'method';
9const INJECTABLE = Symbol('Injectable');
10const ROUTE = Symbol('Route');
11
12const Injectable = (): ClassDecorator => target => {
13  Reflect.defineMetadata(INJECTABLE, true, target);
14};
15const isInjectable = <T>(constructor: Constructor<T>) => {
16  return !!Reflect.getMetadata(INJECTABLE, constructor);
17};
18const isRoute = (target: any) => {
19  return !!Reflect.getMetadata(ROUTE, target);
20};
21
22const Controller = (basePath: string): ClassDecorator => target => {
23  Injectable()(target);
24  Reflect.defineMetadata(PATH_MATA, basePath, target);
25};
26
27const createRoute = (method: string) => (path: string): MethodDecorator => (target, propertyKey, descriptor: TypedPropertyDescriptor<any>) => {
28  const type = Reflect.getMetadata('design:type', target, propertyKey);
29  if (type === Function) {
30    Reflect.defineMetadata(ROUTE, true, descriptor.value);
31    Reflect.defineMetadata(METHOD_MATA, method, descriptor.value);
32    Reflect.defineMetadata(PATH_MATA, path, descriptor.value);
33  }
34};
35
36const Get = createRoute('get');
37const Post = createRoute('post');
38
39function mappingRoutes(instance: any) {
40  const prototype = Object.getPrototypeOf(instance);
41  const methodNames = Object.getOwnPropertyNames(prototype).filter(name => isRoute(prototype[name]));
42  const basePath = Reflect.getMetadata(PATH_MATA, instance.constructor);
43  return methodNames.map(name => {
44    const fn = prototype[name];
45    return {
46      basePath,
47      method: Reflect.getMetadata(METHOD_MATA, fn),
48      route: Reflect.getMetadata(PATH_MATA, fn),
49      fn,
50      name,
51    };
52  });
53}
54
55export function factory<T>(target: Constructor<T>): T {
56  if (!isInjectable(target)) {
57    throw new Error(`${target.name} must be injectable`);
58  }
59  const providers = Reflect.getMetadata('design:paramtypes', target) || [];
60  const args = providers.map((provider: Constructor) => factory(provider));
61  return new target(...args);
62}
63
64@Controller('/api')
65class TestController {
66  @Get('/list')
67  getList() {
68    return 'this is a list';
69  }
70  @Post('/create')
71  create() {
72    return 'create an item';
73  }
74}
75
76export const test = mappingRoutes(factory(TestController));

Reflect Metadata

什么是Reflect metadata

TS配置

安装reflect-metadata

示例

依赖注入 DI

Controller 控制器