7 replies

TS, derive type from key of another type

Let's say we have this type

type DataFile = {
  name: string;
  id: number;
  category: 'cat' | 'dog'
} | null

type DataFile = {
  name: string;
  id: number;
  category: 'cat' | 'dog'
} | null

and elsewhere I want to have another type:

type DataDisplay = {
  name: string;
  id: number;
  category: ...
}

type DataDisplay = {
  name: string;
  id: number;
  category: ...
}

I want the

category

category

DataDisplay

DataDisplay

to also be

'cat' | 'dog'

'cat' | 'dog'

but I want to know if there's a way to have it be derived from

DataFile

DataFile

so if that changes, the

DataDisplay

DataDisplay

will automatically account for that. like

DataFile['category']

DataFile['category']

but that doesn't work because of the

| null

| null

Solution

sorry, I forgot to actually post the simpler way lmao:

type DataDisplay = {
  name: string;
  id: number;
  category: Exclude<DataFile, null>['category']
}

type DataDisplay = {
  name: string;
  id: number;
  category: Exclude<DataFile, null>['category']
}