ternary operator with an empty object always gives an empty object

[zpdDG4gta8XKpMCd]

const data = Math.random() > 0.5 ? { value: 1 } : { }; 
// expected data to be {} | { value: number }, actual data is {}

[gcnew]

I think its caused by subtype reduction. Unfortunately {} is really poisonous.

I've stumbled upon a similar issue, where because of #13039 (comment) the reduction is unsafe: #12970.

[jurosh]

It's really dangerous, also code like this which looks to be properly typed can silently introduce errors to codebase:

interface IObject {
  foo?: boolean;
}

const fooBar: IObject = true ? {
  foo: 'not boolean', // should be boolean only
  notExisting: '132' // should not exist
} : {};

It's always taking {}, so we can type everything into fooBar, no matter that we strictly defined IObject as constant type.

[mhegazy]

{} is a super type of {value: number}, and {} | {value:number} is the same as {} from assignability point of view.

[zpdDG4gta8XKpMCd]

by the same logic 6 | false is {} too which is a super type

[mhegazy]

well, yes, {} is the top type.

[zpdDG4gta8XKpMCd]

i love your sense of humor, dear sir

[OliverJAsh]

How come this behaviour only applies to ternary operators, not functions?

    // expected error, but got none!
    const x2: { blur?: string } = 'foo' ? { blur: 1 } : {};

    // expected error, got error
    const x3: { blur?: string } = (() => {
        if ('foo') {
            return { blur: 1 };
        } else {
            return {};
        }
    })();

[RyanCavanaugh]

Tracking this at #19236