typescript - 如何在 TypeScript 中为装饰器添加可选参数？

Question

我想创建一个可以选择接受参数的字段装饰器。
参数应包含以下任何值:nothing、 bool 值或函数。
我知道该怎么做，但我对结果不是 100% 满意:

export class TestClass{

   @Required(isRequired) 
   public testField: string;

}

export function isRequired():boolean{
   ... some validation logic, maybe depending on other fields...
   return result;
}

@Required 的实现:

export function Required(expression?: boolean|Function): Function {
    return (target: any, key: string) => {
        if (expression === null || typeof expression == 'undefined') {
            expression = true;
        }
        console.log("Required found: " + expression, ":", target, key);
        ... register the field and its validation expression for later usage
    }
}

所以这很好用，但是当我不想添加表达式(并因此使用默认的“true”表达式)时，我希望能够像这样编写它:

class TestClass{

   @Required
   public testField: string;

}

我收到一个 TypeScript 错误 (TS1240) 说:

Unable to resolve signature of property decorator when called as an expression. Supplied parameters do not match any signature of call target

所以我需要写@Required()

class TestClass{

   @Required()
   public testField: string;

}

是否可以编写一个可选参数的装饰器实现，并且当未指定该参数时，不需要添加 "()"？

Answer 1

实际上，这是可能的。

这是一个工作示例:

export type Target = {
  new (...args: any[]): any,
  name: string
};

export function Component(target: Target): void;
export function Component(name: string): (target: Target) => void;
export function Component(nameOrTarget: string | Target) {
  if (typeof nameOrTarget !== 'string') {
    console.log(nameOrTarget.name, ' is now decorated');
  } else {
    return function (target: Target) {
      const name = nameOrTarget || target.name;
      console.log(name, ' is now decorated');
    };
  }
}

@Component
export class MyDatabase { }

@Component('Hello Db')
export class MyHelloDatabase { }

最重要的部分是以下两行:

export function Component(target: Target): void;
export function Component(name: string): (target: Target) => void;

如果有人在寻找更多信息，请查看 GitHub issue .