TypeScript：在编译时使用枚举作为接口/对象键的过滤器

Question

Question

I have an enum (string to string) that contains valid keys for a function . I also have an object (or interface ) that has some keys in the enum, and some not.

How can I set the parameter of my function to only be only the keys from the interface that exist in the enum ? (eg Pick, Extract, Intersection, whatever you wanna call them, that properly preserves the keys.)

Example

The following example is irrelevant to my project, but proper exhibits my need.

Let's say the enum and the interface are as following:

enum PromotableProperties {
  SALARY = "salary",
  SIGNON_BONUS = "signonBonus",
  ANNUAL_BONUS = "annualBonus",
}

interface IExistingEmployee {
  id:           number;
  name:         string;
  salary:       number;
  signonBonus:  number;
  age:          number;
}

Now the actual code is:

type ValidPropsOf<ENUM_T, OBJ_T> = ...; // I want this!

type PromotablePropsForExistingEmployee = ValidPropsOf<PromotableProperties, IExistingEmployee>;


function promoteEmployeeBy(
  emp: IExistingEmployee,
  prop: ValidPropsOf<PromotableProperties, IExistingEmployee>,
  byValue: number,
): void {
  emp[prop] += byValue;
  console.log(`${emp.name}'s ${prop} is increase by ${byValue}'`);
}

const goodOldJohn: IExistingEmployee = {
  id: 5,
  name: "john",
  salary: 20000,
  signonBonus: 1000,
  age: 25,
};

promoteEmployeeBy(goodOldJohn, PromotableProperties.SALARY, 100);
promoteEmployeeBy(goodOldJohn, PromotableProperties.ANNUAL_BONUS, 100); // Error
promoteEmployeeBy(goodOldJohn, "age", 100); // Error

Note that the second function call should fail, because ANNUAL_BONUS doesn't exist in the IExistingEmployee , and the third call should fail because age is not in PromotableProperties .

What I need

... is the utility type of type ValidPropsOf<ENUM_T, OBJ_T> = ... the returns the keys that exist in both the enum (as value) and the object/interface.

TS Playground

here .

Answer 1

What didn't work

I assumed Extract (from the TS official Utility Types ) should work, but I couldn't get it to work.

I also tried Pick and a bunch of other utility types from the two known TS Utility repos, I knew of, but none helped.

1. https://github.com/piotrwitek/utility-types
2. https://github.com/krzkaczor/ts-essentials

What did work

What did work for me was a double Exclude ! It was:

type ValidPropsOf<ENUM_T, OBJ_T> = Exclude<ENUM_T, Exclude<ENUM_T, keyof OBJ_T>>;

Apparently Exclude preserves the keys properly (and doesn't aggressively generalize individual keys). So From the enum I take out the ones that don't exist in the object (call them badProps ), and the the good ones would be goodProps = allProps - badProps .

It completely preserved the individual keys. You can test it by hovering over the type in the function in this working TS Playground Link .