useAsyncValue

import { useAsyncValue } from "@prestojs/util";

useAsyncValue(props)

Resolve a value from an id using an async function.

For the specified id the resolve function will be called and should return the value for the specified id.

For multiple values see documentation below.

	Parameter	Type	Description
	props.existingValues	T[]	An optional array of existing values to try and find the value in. If each item does not implement Identifiable then you must provide the `getId` function. You can use this to avoid resolving data that already exists. If dealing with ViewModel instances you can use it with useViewModelCache, eg. const existingValues = useViewModelCache(User, cache => cache.get(id, fieldNames)); const { value } = useAsyncValue({ id, existingValues, resolve: fetchUser });
	props.getId	Function	A function that returns a unique ID for each item in `existingValues`. Only required if each item does not implement Identifiable.
	props.onError	Function	Called when `resolve` errors. Passed the error returned from `resolve`.
	props.onSuccess	Function	Called when `resolve` resolves successfully. Is passed a single parameter which is the value returned from `resolve`
	props.trigger	"MANUAL"\|"DEEP"	When to trigger the fetch. Defaults to `DEEP` which means whenever `id` or `ids` changed it will refetch if the value hasn't already been resolved. If set to `MANUAL` nothing will happen until it changes to `DEEP`. You can use this to defer execution until the value is required.
*	props.id	Id\|null	Single `id` for value to fetch or null if nothing yet to resolve. If you need to resolve multiple values use the other form documented below passing `ids` instead.
*	props.resolve	Function	Resolve the value for the provided ID. Function is passed a single parameter being `id`. Note that when `trigger` is `DEEP` changes to this function will cause it to be called again so you must memoize it (eg. with `useCallback`) if it's defined in your component or hook.

Returns

UseAsyncValueReturn

Key	Type	Description
error	null\|Error	Set to the rejected value of the promise. Only one of `error` and `value` can be set. If `isLoading` is true consider this stale (ie. based on previous props). This can be useful when you want the UI to show the previous value until the next value is ready.
isLoading	boolean	True while `resolve` call is in progress.
reset	Function	When called will set both result and error to null. Will not immediately trigger a call to the action but subsequent changes to query or paginator will according to the value of `trigger`. If value is found in `existingValues` then it will still be returned even if you call `reset` - `reset` only clears values that are returned from `resolve`.
run	Function	A function to manually trigger the action. If `options.trigger` is `MANUAL` calling this function is the only way to trigger the action. This function will return a promise that resolves/rejects to same value returned by `execute`. If `accumulatePages` is set the value returned is the accumulated value.
value	T\|null	The resolved value

useAsyncValue(props)

Resolve values from an array of ids using an async function.

For the specified array of ids the resolve function will be called and should return an array of the same size with each entry being the resolved value for the corresponding id.

If existingValues is provided this will be consulted first before calling resolve. This is useful when you have a list of values that may or may not have the data you care about. If it's there then the values will be returned immediately. Note that if any of the ids are missing from existingValues then it will be ignored and a call to resolve will be made requesting values for all ids.

	Parameter	Type	Description
	props.existingValues	T[]	An optional array of existing values to try and find the value in. If each item does not implement Identifiable then you must provide the `getId` function. You can use this to avoid resolving data that already exists. If dealing with ViewModel instances you can use it with useViewModelCache, eg. const existingValues = useViewModelCache(User, cache => cache.get(id, fieldNames)); const { value } = useAsyncValue({ id, existingValues, resolve: fetchUser });
	props.getId	Function	A function that returns a unique ID for each item in `existingValues`. Only required if each item does not implement Identifiable.
	props.onError	Function	Called when `resolve` errors. Passed the error returned from `resolve`.
	props.onSuccess	Function	Called when `resolve` resolves successfully. Is passed a single parameter which is the value returned from `resolve`
	props.trigger	"MANUAL"\|"DEEP"	When to trigger the fetch. Defaults to `DEEP` which means whenever `id` or `ids` changed it will refetch if the value hasn't already been resolved. If set to `MANUAL` nothing will happen until it changes to `DEEP`. You can use this to defer execution until the value is required.
*	props.ids	Id[]\|null	Array of ids to resolve values for or null if nothing yet to resolve If you need to resolve a single value use the other form documented above passing `id` instead
*	props.resolve	Function	Resolve the value for the provided IDs. Function is passed a single parameter being `ids`

Returns

UseAsyncValueReturn

Key	Type	Description
error	null\|Error	Set to the rejected value of the promise. Only one of `error` and `value` can be set. If `isLoading` is true consider this stale (ie. based on previous props). This can be useful when you want the UI to show the previous value until the next value is ready.
isLoading	boolean	True while `resolve` call is in progress.
reset	Function	When called will set both result and error to null. Will not immediately trigger a call to the action but subsequent changes to query or paginator will according to the value of `trigger`. If value is found in `existingValues` then it will still be returned even if you call `reset` - `reset` only clears values that are returned from `resolve`.
run	Function	A function to manually trigger the action. If `options.trigger` is `MANUAL` calling this function is the only way to trigger the action. This function will return a promise that resolves/rejects to same value returned by `execute`. If `accumulatePages` is set the value returned is the accumulated value.
value	T\|null	The resolved value