I have [something akin to] this:
type Thunk = 'uh' | 'um' | 'dunno mate';
interface Whatever {
meh: Thunk;
}
And that’s all good my bro. But then later I need this:
interface LoadsOfWhatever {
meh: Thunk[];
}
Is there a way to extend/Pick/etc it from Whatever or will this just need to be literally created?
>Solution :
This can be done with mapped types. These let you calculate a new type from an old one, applying some transformation to every property. Here’s how it looks to turn every property into an array:
type Thunk = 'uh' | 'um' | 'dunno mate';
interface Whatever {
meh: Thunk;
}
type LoadsOfWhatever = {
[key in keyof Whatever]: Whatever[key][];
}
Obviously it’s wordier than the original code if all you have is the one meh property. But if Whatever had 50 properties, you wouldn’t need to change LoadsOfWhatever; it would turn all 50 properties into arrays