[Suggestion] Global object properties should not surface on type level indexing

[gcnew]

TypeScript Version: nightly (2.6.0-dev.20170829)

Code

type Point = { x: number, y: number }
type Mapped = Record<'x'|'y', number>
type IndexSignature = { [x: string]: never }

// All of the following have type: `() => Object`
type Test1 = Point['valueOf']
type Test2 = Mapped['valueOf'] 
type Test3 = IndexSignature['valueOf']

Expected behavior:
Test1, Test2 and Test3 should all be errors.

User provided types should be considered "exact". No properties should be inherited from Object. The current behaviour is of little use, however it's quite confusing and really gets in the way of type level programming.

[gcnew]

The magic Object keys are not present in keyof expressions, causing non-uniform behaviour:

type ValueOf<T, K extends keyof T> = T[K]
type Test4 = ValueOf<1, 'constructor'> // error
type Test5 = 1['constructor']          // OK 

[olegdunkan]

#16578 (comment)

[mhegazy]

It is consistent with other uses of indexing.. e.g. indexing with numbers.. keyof T will return you only string, public, and own properties. I would argue that this is exactelly what you want.. you do not want toString to start showing up in all keyof T... that would be too verbose, and would be a breaking change..

On the flip side, not having it in keyof T does not change the fact that toString exists on all objects.. this is in a sense similar to indexing with numbers.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.