如何在 function 中使用 generics 获得嵌套接口值？

Question

I have a Typescript interface:

export interface AwesomeInterface {
  hooks?: {
    beforeCreate?: AwesomeFunction1;
    beforeUpdate?: AwesomeFunction2;
  };
}

Now I want to write a function that takes one of beforeCreate or beforeUpdate as a string and returns a function that will be of type AwesomeFunction1 or AwesomeFunction2 based on what the input was.

export const getFieldTypesHook = <T extends keyof NonNullable<FieldTypeConfig['hooks']>>(
  name: T,
): FieldTypeConfig['hooks'][T] => {
  ...
};

However, I get an error saying

Type 'T' cannot be used to index type '{ beforeCreate?: AwesomeFunction1 | undefined; beforeUpdate?: AwesomeFucntion2 | undefined }`

How do I make this happen?

Answer 1

export interface AwesomeInterface {
    hooks: {
        beforeCreate: string;
        beforeUpdate: number;
    };
}

const hooks: AwesomeInterface = {
    hooks: {
        beforeCreate: '5',
        beforeUpdate: 5
    }
}

export const getFieldTypesHook = <T extends keyof AwesomeInterface['hooks']>(
    name: T,
): AwesomeInterface['hooks'][T] => {
    return hooks.hooks[name];
};