🔎 搜索词

decorator, experimentalDecorators, emitDecoratorMetadata, TC39, reflect-metadata, Reflect.metadata(k, v)

🕗 版本与回归信息

当设置禁用实验性装饰器时出现问题

"experimentalDecorators": false,
"emitDecoratorMetadata": false,

⏯ Playground链接

https://github.com/paulsmithkc/typescript-decorators

💻 代码

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2021",
    "module": "commonjs",
    "outDir": "dist",
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false
  },
  "include": ["src"],
  "exclude": ["node_modules", "dist"]
}

src/index.ts

import 'reflect-metadata';

function setting(defaultValue: string): any {
  function getType(target: unknown, property: string | symbol) {
    return Reflect.getMetadata('design:type', target, property);
  }
  function settingExperimental(target: unknown, property: string | symbol): void {
    console.log('settingExperimental', { defaultValue, target, property, type: getType(target, property) });
    target[property] = process.env[String(property)] || defaultValue;
    return;
  }
  function settingTC39(_target: unknown, context: ClassFieldDecoratorContext): () => string {
    return function (): string {
      console.log('settingTC39', { defaultValue, target: this, context, type: getType(this, context.name) });
      return process.env[String(context.name)] || defaultValue;
    };
  }
  return function (target: unknown, context: string | symbol | ClassFieldDecoratorContext) {
    if (typeof context !== 'object') {
      return settingExperimental(target, context);
    } else {
      return settingTC39(target, context);
    }
  };
}

class Config {
  @setting('default_1') SETTING_ONE: string;
}
const configInstance = new Config();

运行方式：

tsc --project tsconfig.json && node dist/index.js

🙁 实际行为

Reflect.getMetadata('design:type', target, property) 返回 undefined。

🙂 预期行为

Reflect.getMetadata('design:type', target, property) 在使用标准 TC39 装饰器时，返回类字段的类型。

关于问题的附加信息

1. 使用以下方式进行转译时：

"experimentalDecorators": true,
"emitDecoratorMetadata": true,

装饰器 Reflect.metadata("design:type", type) 会自动应用于每个类字段。

1. 使用以下方式进行转译时：

"experimentalDecorators": false,
"emitDecoratorMetadata": false,

装饰器 Reflect.metadata("design:type", type) 不会被应用。

1. 使用以下方式进行转译时：

"experimentalDecorators": false,
"emitDecoratorMetadata": true,

Typescript 产生以下错误

Option 'emitDecoratorMetadata' cannot be specified without specifying option 'experimentalDecorators'.