Question: Is there a simple way to get a type reduced to only primitives?

For example, if I have a type that is:

type Company = {
  name: string
  employees: Person[]
}

type Person = {
  name: string
  age: number
}

How can I get the deeply interpreted type, so that in Company instead of a reference to another type alias I get the properties of Person in there.

[zaripych]

I’m currently solving exactly same problem and I wrote a little script for it. My use case is to build a function that makes it more explicit which API’s a given shared type affects - when changed. So if you changed a type - you will see all the public boundary interface functions/api this change affects because it would lead to a jest snapshot change.

E.g. for this type:

type TestType = {
	optionalPrimitive?: string;
	nested: NestedType;
	get getterProp(): number;
	pick: Pick<PickAndChooseSource, 'first' | 'fourth'>;
	omit?: Omit<PickAndChooseSource, 'first' | 'fourth'>;

	functionCall(): void;
	callWithPromise: () => Promise<void>;
	callWithParams(param: { first: string; second: number }): number;
	callWithParams2(
		param: { first: string; second: number },
		deps: { properties: boolean },
	): number;

	num: number;
};

it prints:

{ 
  optionalPrimitive?: undefined | string; 
  nested: { 
    stringLiterals: 'success' | 'failed'; 
    simpleArray: string[]; 
    complexArray?: undefined | Array< 
      { 
        key: 'string'; 
        value: number; 
      } 
    >; 
    intersection: { 
      ok: true; 
    } & { 
      ok: false; 
    }; 
    tuple: [ 
      number, 
      string, 
      { 
        str: string; 
      } 
    ]; 
  }; 
  getterProp: number; 
  pick: { 
    first: number; 
    fourth: null | { 
      scissor: string; 
      paper: string; 
      rock: string; 
    }; 
  }; 
  omit?: undefined | { 
    second: string; 
    third: null; 
  }; 
  functionCall(): void 
  callWithPromise(): Promise<void> 
  callWithParams(param: { 
    first: string; 
    second: number; 
  }): number 
  callWithParams2(param: { 
    first: string; 
    second: number; 
  }, deps: { 
    properties: boolean; 
  }): number 
  value: { 
    str: string; 
    num: number; 
  }; 
} 

This is my first attempt at this and the first time I’m using ts-morph - I welcome any feedback 👍 https://gist.github.com/zaripych/963fa6584524e5b446b70548dbabbf65

I’m almost there, but currently have a problem for properties that do not have declared types. E.g. getDeclarations() returns an empty array. 🤯 Does anybody know if there is an additional way to get a property type?

[DaniGuardiola]

@zaripych you just helped me fix a problem in which types created with Omit where missing keys. I fixed it by doing getTypeAtLocation, just like you. Thanks a lot!