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TypeScript 元数据操作 API 及示例

1. 配置环境

安装依赖

npm install reflect-metadata

tsconfig.json 配置

{"compilerOptions": {"experimentalDecorators": true,"emitDecoratorMetadata": true,"target": "ES6"}
}

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2. 元数据操作 API

• Reflect.defineMetadata(key, value, target, propertyKey?)
• Reflect.getMetadata(key, target, propertyKey?)
• Reflect.hasMetadata(key, target, propertyKey?)
• Reflect.getMetadataKeys(target, propertyKey?)

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3. 内置元数据键

• design:type：属性/方法的类型
• design:paramtypes：方法参数的类型
• design:returntype：方法返回值类型

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4. 示例代码

示例 1：自定义装饰器

import "reflect-metadata";function LogInfo(message: string) {return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {Reflect.defineMetadata("log-message", message, target, propertyKey);};
}class UserService {@LogInfo("Fetching user data")getUser(id: number) {return { id, name: "Alice" };}
}const message = Reflect.getMetadata("log-message", UserService.prototype, "getUser");
console.log(message); // 输出: "Fetching user data"

示例 2：内置元数据推断

import "reflect-metadata";class Example {@Reflect.metadata("custom-prop", true)public name: string = "";greet(@Reflect.metadata("required", true) name: string): string {return `Hello, ${name}`;}
}const propType = Reflect.getMetadata("design:type", Example.prototype, "name");
console.log(propType); // 输出: [Function: String]const paramTypes = Reflect.getMetadata("design:paramtypes", Example.prototype, "greet");
console.log(paramTypes); // 输出: [ [Function: String] ]

示例 3：类级别元数据

import "reflect-metadata";@Reflect.metadata("api-version", "1.0.0")
class ApiController {@Reflect.metadata("http-method", "GET")public fetchData() {}
}const apiVersion = Reflect.getMetadata("api-version", ApiController);
console.log(apiVersion); // 输出: "1.0.0"const httpMethod = Reflect.getMetadata("http-method", ApiController.prototype, "fetchData");
console.log(httpMethod); // 输出: "GET"

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5. 应用场景

• ​依赖注入 (DI)
• ​序列化/验证
• ​Web 框架路由
• ​ORM 映射