TypeScript doesn't warn me that a property is missing

[anas-araid]

Bug Report

⏯ Playground Link

Playground link with relevant code

💻 Code

type DataType = {
  value: (Data & Extra) | Data;
};

type Data = {
  type1: string;
};

type Extra = {
  isEditable: boolean;
  onChange: () => void;
};

const data: DataType = {
  // value should throw an error (onChange is not specified)
  value: {
    type1: 'type',
    isEditable: true,
  },
};

🙁 Actual behavior

TypeScript ignores this definition ((Data & Extra) | Data)

🙂 Expected behavior

I expect TypeScript to warn me that a property within value is missing: e.g (onChange is not specified)

[fatcerberus]

The value you've provided is not a valid Data & Extra, but it is a valid Data (the types aren't exact, objects can have extra properties). Since the type of .value is (Data & Extra) | Data, there is no type error in this code.

[fatcerberus]

Just to reiterate/clarify: Because objects can have more properties than their type calls for, unions of object types are not mutually exclusive. If you want a mutually exclusive type you need to use a discriminated union.

[MartinJohns]

Also related: #20863

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.