Expanding the capabilities of indexable types in Typescript

I recently created an interface for form validation. Here is the initial structure:

export interface SearchBarValidatorObj {
  [k: string]: KeyObjectValidator;
}

However, I am wondering if there is a way to add a "static" type to it in order to achieve certain functionality. Would this modified version work?

export interface SearchBarValidatorObj {
  required: string | boolean
  [k: string]: KeyObjectValidator;
}

For reference, here is the KeyObjectValidator interface definition:

interface KeyObjectValidator {
  value: string | number | RegExp;
  message?: string;
}

Cheers!

Answer №1

A good approach would be to implement an intersection type in this scenario:

export interface SearchBarValidatorObj {
  [k: string]: KeyObjectValidator;
}

interface KeyObjectValidator {
  value: string | number | RegExp;
  message?: string;
}

type WithStatic = SearchBarValidatorObj & { required: string | boolean };

let obj!: WithStatic;
// these assignments are considered valid
obj.required = false;
obj.a = { value: 5 };

// meanwhile, the following assignments are not valid
obj.required = 4;
obj.required = { value: 5 };

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