Object returned from a function can have keys not present in its return type #50064
Description
Bug Report
When a function is typed to return an object of a certain type, the properties of the object can be expanded, meaning extra properties can be added to the ones described in the type or interface.
🔎 Search Terms
function return object type
🕗 Version & Regression Information
This is observable on the playground in all available versions.
Couldn't find anything I understood to be relevant in https://github.com/Microsoft/TypeScript/wiki/FAQ#common-bugs-that-arent-bugs
- This is a crash: No
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about interfaces and types of function return values
⏯ Playground Link
💻 Code
interface Result {
foo: string;
}
type Func = () => Result
const noError:Func = () => ({
foo: 'string1',
// @ts-expect-error
bar: 2,
});
const error:Func = (): Result => ({
foo: 'string1',
// @ts-expect-error
bar: 2,
});
const error2:Func = (): ReturnType<Func> => ({
foo: 'string1',
// @ts-expect-error
bar: 2,
});🙁 Actual behavior
Extra properties in the returned object, which aren't defined in the interface or type, do not raise an error.
🙂 Expected behavior
Extra properties in the returned object, which aren't defined in the interface or type, should raise an error.