# State properties

These are returned in an object by `useAsync()` or provided by `<Async>` as render props to the `children` function:

* [`data`](#data) Last resolved promise value, maintained when new error arrives.
* [`error`](#error) Rejected promise reason, cleared when new data arrives.
* [`value`](#value) The value of `data` or `error`, whichever was last updated.
* [`initialValue`](#initialvalue) The data or error that was provided through the `initialValue` prop.
* [`startedAt`](#startedat) When the current/last promise was started.
* [`finishedAt`](#finishedat) When the last promise was fulfilled or rejected.
* [`status`](#status) One of: `initial`, `pending`, `fulfilled`, `rejected`.
* [`isInitial`](#isinitial) true when no promise has ever started, or one started but was cancelled.
* [`isPending`](#ispending) true when a promise is currently awaiting settlement. Alias: `isLoading`
* [`isFulfilled`](#isfulfilled) true when the last promise was fulfilled. Alias: `isResolved`
* [`isRejected`](#isrejected) true when the last promise was rejected.
* [`isSettled`](#issettled) true when the last promise was fulfilled or rejected (not initial or pending).
* [`counter`](#counter) The number of times a promise was started.
* [`promise`](#promise) A reference to the internal wrapper promise, which can be chained on.
* [`run`](#run) Invokes the `deferFn`.
* [`reload`](#reload) Re-runs the promise when invoked, using any previous arguments.
* [`cancel`](#cancel) Cancel any pending promise.
* [`setData`](#setdata) Sets `data` to the passed value, unsets `error` and cancels any pending promise.
* [`setError`](#seterror) Sets `error` to the passed value and cancels any pending promise.

## `data`

> `any`

Last resolved promise value, maintained when new error arrives.

## `error`

> `Error`

Rejected promise reason, cleared when new data arrives.

## `value`

> `any | Error`

The data or error that was last provided (either through `initialValue` or by settling a promise).

## `initialValue`

> `any | Error`

The data or error that was originally provided through the `initialValue` prop.

## `startedAt`

> `Date`

Tracks when the current/last promise was started.

## `finishedAt`

> `Date`

Tracks when the last promise was resolved or rejected.

## `status`

> `string`

One of: `initial`, `pending`, `fulfilled`, `rejected`. These are available for import as `statusTypes`.

## `isInitial`

> `boolean`

`true` while no promise has started yet, or one was started but cancelled.

## `isPending`

> `boolean`

`true` while a promise is pending (loading), `false` otherwise.

Alias: `isLoading`

## `isFulfilled`

> `boolean`

`true` when the last promise was fulfilled (resolved to a value).

Alias: `isResolved`

## `isRejected`

> `boolean`

`true` when the last promise was rejected.

## `isSettled`

> `boolean`

`true` when the last promise was either fulfilled or rejected (i.e. not initial or pending)

## `counter`

> `number`

The number of times a promise was started.

## `promise`

> `Promise`

A reference to the internal wrapper promise created when starting a new promise (either automatically or by invoking `run` / `reload`). It fulfills or rejects along with the provided `promise` / `promiseFn` / `deferFn`. Useful as a chainable alternative to the `onResolve` / `onReject` callbacks.

Warning! If you chain on `promise`, you MUST provide a rejection handler (e.g. `.catch(...)`). Otherwise React will throw an exception and crash if the promise rejects.

## `run`

> `function(...args: any[]): void`

Runs the `deferFn`, passing any arguments provided as an array.

When used with `useFetch`, `run` has several overloaded signatures:

> `function(override: OverrideParams | (params: OverrideParams) => OverrideParams): void`
>
> `function(event: SyntheticEvent | Event): void`
>
> `function(): void`

Where `type OverrideParams = { resource?: RequestInfo } & Partial<RequestInit>`.

This way you can run the `fetch` request with custom `resource` and `init`. If `override` is an object it will be spread over the default `resource` and `init` for `fetch`. If it's a function it will be invoked with the params defined with `useFetch`, and should return an `override` object. This way you can either extend or override the value of `resource` and `init`, for example to change the URL or set custom request headers.

## `reload`

> `function(): void`

Re-runs the promise when invoked, using the previous arguments.

## `cancel`

> `function(): void`

Cancels the currently pending promise by ignoring its result and calls `abort()` on the AbortController.

## `setData`

> `function(data: any, callback?: () => void): any`

Function that sets `data` to the passed value, unsets `error` and cancels any pending promise. Takes an optional callback which is invoked after the state update is completed. Returns the data to enable chaining.

## `setError`

> `function(error: Error, callback?: () => void): Error`

Function that sets `error` to the passed value and cancels any pending promise. Takes an optional callback which is invoked after the state update is completed. Returns the error to enable chaining.