Typescript generics: How to define properties

Question

I'm struggling a bit with generics in typescript and just encountered the following

save<T>(data: T): Observable<T> { 
    const created = data.createdTime;
    ...
}

The problem here is that typescript tells me that createdTime is an unknown property. However, in my case, any data object passed to save will have a createdTime property. What is the correct way to tell typescript that data has this property ?

Answer 1

Make T extend an interface

interface Data {
    createdTime: number
}

save<T extends Data>(data: T): Observable<T> { 
    const created = data.createdTime;
    ...
}