I’m trying to apply a type if the object has x. What I tried had unexpected results. Can anyone explain the results and/or offer a solution?

interface BaseType {
  x?: number;
  a?: string;
  b?: number;
}

interface WithoutX extends Omit<BaseType, "x"> {
  
};

interface WithX extends Omit<BaseType, "x"> {
  x: any;
  y: string;
};

type ConditionalType = WithX | WithoutX;

// No `x` or `y`, conforms to WithoutX
const validObject1: ConditionalType = {
  a: "hello",
  b: 42
};

// Has `x` and `y`, conforms to WithX
const validObject2: ConditionalType = {
  a: "world",
  x: 10,
  y: "required"
};

// This should cause a type error because `y` is required if `x` is present
const shouldBeInvalidButIsNot: ConditionalType = {
  a: "typescript",
  x: 10
};

const invalidObjectBecauseX: WithoutX = {
  a: "typescript",
  x: 10
};

const invalidObjectBecauseYMissing: WithX = {
  a: "typescript",
  x: 10
};

Playground