I have a loadMore function that retrieves data and returns a Promise of either Project[] or Folder[] or undefined.
const items = await loadMore();
How can I specifically cast the type of 'items' to Folder[] in TypeScript?
I have a loadMore function that retrieves data and returns a Promise of either Project[] or Folder[] or undefined.
const items = await loadMore();
How can I specifically cast the type of 'items' to Folder[] in TypeScript?
In my opinion, it is more effective to distinguish the elements of the array by using an inline type discriminator as the condition in Array.filter
const folderItems = items?.filter(
(v: Folder | Project): v is Folder => /* Is v actually a Folder? true/false */
);
This will result in providing you with either an array that exclusively contains Folder
items or undefined
if the value of items
is undefined
.
Here's an alternative method you could use:
let folders: Folder[] = getFolders()
When working with TypeScript, one way to ensure type safety is through a type assertion:
const items = await loadMore() as Folder[];
However, it is recommended to utilize discriminated unions for enhanced safety.
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