TypeScript:从装饰器推断返回类型? [英] TypeScript: Inferring return type from a Decorator?

问题描述

当装饰器更改其返回类型时，如何让 TypeScript 推断装饰方法的类型?

How do I get TypeScript to infer the Type of a decorated method when the decorator changes it's return type?

在下面的基本示例中，我装饰了一个返回字符串化对象的方法:

In the basic example below, I decorate a method to return a stringified object:

function jsonStringify() {
  return function (target, decoratedFnName: string, descriptor: PropertyDescriptor) {
    let decoratedFn = descriptor.value;

    let newFn = function () {
      let object = decoratedFn.apply(target, arguments);

      return JSON.stringify(object);
    };

    descriptor.value = newFn;

    return descriptor;
  }
}

class Decorated {
  @jsonStringify()
  method(name: string, description: string) {
    return {
      name: name,
      description: description
    }
  }
};

let stringifiedObject = new Decorated().method('Test Name', 'Test Description');

console.log(stringifiedObject.includes('Test Name'));

如果我在 tsconfig.json 中使用 "noEmitOnError": false 转译 TypeScript，那么代码会完美运行并将 true 记录到控制台.但是，tsc 抱怨错误:

If I transpile the TypeScript with "noEmitOnError": false in tsconfig.json, then the code runs perfectly and logs true to the console. However, tsc complains with the error:

error TS2339: Property 'includes' does not exist on type '{ name: string; description: string; }'.

我理解这是因为 Decorated.method() 返回一个对象而不是一个字符串，但是这个方法有一个返回一个字符串的装饰器.我需要做什么才能让 TypeScript 从装饰器推断类型?

Which I understand because Decorated.method() returns an object and not a string, but this method has a decorator which returns a string. What do I need to do to get TypeScript to infer the type from the decorator?

推荐答案

目前不支持使用装饰器更改函数的返回类型.

It is not currently supported to change the return type of a function with a decorator.

在 github 上有一个 未解决的问题

There is an open issue on github tracking this

作为替代方案，您或许可以这样做:

As an alternative, you could perhaps do something like this:

class Decorated {
  @jsonStringify()
  method(name: string, description: string): string | object {
    return {
      name: name,
      description: description
    };
  }
}

const stringifiedObject = new Decorated().method('Test Name', 'Test Description') as string;

console.log((stringifiedObject as string).includes('Test Name'));

但我知道这可能与您想要的有点不同

but I recognise this is probably a bit of a departure from what you were looking for

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