# Helpers

Reduce garbage collection burden.

# pluckFirst

pluckFirst<TArr>(inputs$: Observable<TArr>): Observable<TArr[0]>

Map an Observable of Arraylike to an Observable of the first item.

Type parameters:

  • TArr ArrayLike

Parameters:

Name Type Description
inputs$ Observable<TArr> An Observable of arraylike.

Returns:

Observable<TArr[0]> Observable of the first item.

Examples:

// An Observable of string
const text$ = useObservable(pluckFirst, [props.text])

# pluckCurrentTargetValue

pluckCurrentTargetValue<TEvent>(
  event$: Observable<TEvent>
): Observable<TEvent["currentTarget"]["value"]>

Maps an Observable of DOM events to an Observable of the currentTarget value.

Type parameters:

  • TEvent Event with currentTarget.value.

Parameters:

Name Type Description
event$ Observable<TEvent> An Observable of events.

Returns:

Observable<TEvent["currentTarget"]["value"]> An Observable of event currentTarget.value.

Examples:

const [onChange, textChange$] = useObservableCallback<
 string,
 React.FormEvent<HTMLInputElement>
>(pluckCurrentTargetValue)

# pluckCurrentTargetChecked

pluckCurrentTargetChecked<TEvent>(
  event$: Observable<TEvent>
): Observable<TEvent["currentTarget"]["checked"]>

Maps an Observable of DOM events to an Observable of the currentTarget checked.

Type parameters:

  • TEvent Event with currentTarget.checked.

Parameters:

Name Type Description
event$ Observable<TEvent> An Observable of events.

Returns:

Observable<TEvent["currentTarget"]["checked"]> An Observable of event currentTarget.checked.

Examples:

const [onChange, checked$] = useObservableCallback<
 boolean,
 React.FormEvent<HTMLInputElement>
>(pluckCurrentTargetChecked)

# identity

identity<T>(value: T): T

Returns the first argument it receives.

Type parameters:

  • T Any value.

Parameters:

Name Type Description
value T Any value.

Returns:

T The first argument.

# useRefFn

One-time ref init.

useRefFn<T>(init: function): MutableRefObject<T>

Type parameters:

  • T any.

Parameters:

Name Type Description
init (): T A function that returns a value. Will be called only once.

Returns:

MutableRefObject<T> A Ref object with the returned value.

# useForceUpdate

Force re-renders Component.

useForceUpdate(): () => void

Returns:

() => void A callback which re-renders component when called.