extract
extract
Accepts an array of T extends object and a single key or an array of keys (K extends keyof T).
Returns a new array of objects constructed from provided key or keys.
Example
const cats = [
{ id: 1, type: 'cat', name: 'Fluffy' },
{ id: 2, type: 'cat', name: 'Emma' },
];
const catsWithoutTypes = extract(cats, ['name', 'id']);
// catsWithoutTypes will be:
// [{id: 1, name: 'Fluffy'}, {id: 2, name: 'Emma'}];
Example
// Usage with RxState
// Usage with RxState
export class AnimalsListComponent {
constructor(private state: RxState<ComponentState>, private api: ApiService) {
state.connect(
'animals'
this.api.getAnimals(),
(state, animals) => extract(animals, ['id', 'name'])
);
}
}
Edge cases
extract(
[
{ id: 1, type: 'cat', name: 'Emma' },
{ id: 2, type: 'dog' },
],
['name', 'id', 'type']
) >
[
{ id: 1, type: 'cat', name: 'Emma' },
{ id: 2, type: 'dog', name: undefined },
]; // dog has no name
extract(
[{ id: 1, type: 'cat', name: 'Emma' }, 1, 'string'] as any,
['id', 'name'] as any
) >
[
{ id: 1, name: 'Emma' },
{ id: undefined, name: undefined },
{ id: undefined, name: undefined },
]; // cat had properties but they are not found in 1 and 'string'
extract(null as any, 'prop') > undefined;
extract(items, {} as any) > undefined;
extract(items, [] as any) > undefined;
extract(items, 1 as any) > undefined;
extract(items, undefined as any) > undefined;
Signature
function slice<T extends object, K extends keyof T>(
object: T,
keys: K | K[]
): Pick<T, K>;