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React Async
Handle promises with ease.


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React component and hook for declarative promise resolution and data fetching. Leverages the Render Props pattern and Hooks for ultimate flexibility as well as the new Context API for ease of use. Makes it easy to handle loading and error states, without assumptions about the shape of your data or the type of request.

  • Zero dependencies
  • Works with promises, async/await and the Fetch API
  • Choose between Render Props, Context-based helper components or the useAsync and useFetch hooks
  • Provides convenient isLoading, startedAt, finishedAt, et al metadata
  • Provides cancel and reload actions
  • Automatic re-run using watch or watchFn prop
  • Accepts onResolve and onReject callbacks
  • Supports abortable fetch by providing an AbortController
  • Supports optimistic updates using setData
  • Supports server-side rendering through initialValue
  • Comes with type definitions for TypeScript
  • Works well in React Native too!

Upgrading to v6

Version 6 comes with a breaking change. See Upgrading for details.

Table of Contents

Rationale

React Async is different in that it tries to resolve data as close as possible to where it will be used, while using a declarative syntax, using just JSX and native promises. This is in contrast to systems like Redux where you would configure any data fetching or updates on a higher (application global) level, using a special construct (actions/reducers).

React Async works really well even in larger applications with multiple or nested data dependencies. It encourages loading data on-demand and in parallel at component level instead of in bulk at the route / page level. It's entirely decoupled from your routes, so it works well in complex applications that have a dynamic routing model or don't use routes at all.

React Async is promise-based, so you can resolve anything you want, not just fetch requests.

Concurrent React and Suspense

The React team is currently working on a large rewrite called Concurrent React, previously known as "Async React". Part of this rewrite is Suspense, which is a generic way for components to suspend rendering while they load data from a cache. It can render a fallback UI while loading data, much like <Async.Loading>.

React Async has no direct relation to Concurrent React. They are conceptually close, but not the same. React Async is meant to make dealing with asynchronous business logic easier. Concurrent React will make those features have less impact on performance and usability. When Suspense lands, React Async will make full use of Suspense features. In fact you can already start using React Async right now, and in a later update you'll get Suspense features for free.

Installation

npm install --save react-async

Or with Yarn:

yarn add react-async

This package requires react as a peer dependency. Please make sure to install that as well. If you want to use the useAsync hook, you'll need react@16.8.0 or later.

Upgrading

Upgrade to v6

  • <Async.Pending> was renamed to <Async.Initial>.
  • Don't forget to deal with any custom instances of <Async> when upgrading.

Upgrade to v4

  • deferFn now receives an args array as the first argument, instead of arguments to run being spread at the front of the arguments list. This enables better interop with TypeScript. You can use destructuring to keep using your existing variables.
  • The shorthand version of useAsync now takes the options object as optional second argument. This used to be initialValue, but was undocumented and inflexible.

Usage

React Async offers three primary APIs: the useAsync hook, the <Async> component and the createInstance factory function. Each has its unique benefits and downsides.

As a hook

The useAsync hook (available from React v16.8.0) offers direct access to React Async's core functionality from within your own function components:

import { useAsync } from "react-async"

const loadCustomer = async ({ customerId }, { signal }) => {
  const res = await fetch(`/api/customers/${customerId}`, { signal })
  if (!res.ok) throw new Error(res)
  return res.json()
}

const MyComponent = () => {
  const { data, error, isLoading } = useAsync({ promiseFn: loadCustomer, customerId: 1 })
  if (isLoading) return "Loading..."
  if (error) return `Something went wrong: ${error.message}`
  if (data)
    return (
      <div>
        <strong>Loaded some data:</strong>
        <pre>{JSON.stringify(data, null, 2)}</pre>
      </div>
    )
  return null
}

Using helper components can greatly improve readability of your render functions by not having to write all those conditional returns.

Or using the shorthand version:

const MyComponent = () => {
  const { data, error, isLoading } = useAsync(loadCustomer, options)
  // ...
}

With useFetch

Because fetch is so commonly used with useAsync, there's a dedicated useFetch hook for it:

import { useFetch } from "react-async"

const MyComponent = () => {
  const headers = { Accept: "application/json" }
  const { data, error, isLoading, run } = useFetch("/api/example", { headers }, options)
  // This will setup a promiseFn with a fetch request and JSON deserialization.
}

useFetch takes the same arguments as fetch itself, as well as options to the underlying useAsync hook. The options object takes two special boolean properties: defer and json. These can be used to switch between deferFn and promiseFn, and enable JSON parsing. By default useFetch automatically uses promiseFn or deferFn based on the request method (deferFn for POST / PUT / PATCH / DELETE) and handles JSON parsing if the Accept header is set to "application/json".

As a component

The classic interface to React Async. Simply use <Async> directly in your JSX component tree, leveraging the render props pattern:

import Async from "react-async"

// Your promiseFn receives all props from Async and an AbortController instance
const loadCustomer = ({ customerId }, { signal }) =>
  fetch(`/api/customers/${customerId}`, { signal })
    .then(res => (res.ok ? res : Promise.reject(res)))
    .then(res => res.json())

const MyComponent = () => (
  <Async promiseFn={loadCustomer} customerId={1}>
    {({ data, error, isLoading }) => {
      if (isLoading) return "Loading..."
      if (error) return `Something went wrong: ${error.message}`
      if (data)
        return (
          <div>
            <strong>Loaded some data:</strong>
            <pre>{JSON.stringify(data, null, 2)}</pre>
          </div>
        )
      return null
    }}
  </Async>
)

Using helper components can greatly improve readability of your render functions by not having to write all those conditional returns.

As a factory

You can also create your own component instances, allowing you to preconfigure them with options such as default onResolve and onReject callbacks.

import { createInstance } from "react-async"

const loadCustomer = ({ customerId }, { signal }) =>
  fetch(`/api/customers/${customerId}`, { signal })
    .then(res => (res.ok ? res : Promise.reject(res)))
    .then(res => res.json())

// createInstance takes a defaultProps object and a displayName (both optional)
const AsyncCustomer = createInstance({ promiseFn: loadCustomer }, "AsyncCustomer")

const MyComponent = () => (
  <AsyncCustomer customerId={1}>
    <AsyncCustomer.Fulfilled>{customer => `Hello ${customer.name}`}</AsyncCustomer.Fulfilled>
  </AsyncCustomer>
)

With helper components

Several helper components are available to improve legibility. They can be used with useAsync by passing in the state, or with <Async> by using Context. Each of these components simply enables or disables rendering of its children based on the current state.

import { useAsync, Pending, Fulfilled, Rejected } from "react-async"

const loadCustomer = async ({ customerId }, { signal }) => {
  // ...
}

const MyComponent = () => {
  const state = useAsync({ promiseFn: loadCustomer, customerId: 1 })
  return (
    <>
      <Pending state={state}>Loading...</Pending>
      <Rejected state={state}>{error => `Something went wrong: ${error.message}`}</Rejected>
      <Fulfilled state={state}>
        {data => (
          <div>
            <strong>Loaded some data:</strong>
            <pre>{JSON.stringify(data, null, 2)}</pre>
          </div>
        )}
      </Fulfilled>
    </>
  )
}

As compounds to

Each of the helper components are also available as static properties of <Async>. In this case you won't have to pass the state object, instead it will be automatically provided through Context.

import Async from "react-async"

const loadCustomer = ({ customerId }, { signal }) =>
  fetch(`/api/customers/${customerId}`, { signal })
    .then(res => (res.ok ? res : Promise.reject(res)))
    .then(res => res.json())

const MyComponent = () => (
  <Async promiseFn={loadCustomer} customerId={1}>
    <Async.Loading>Loading...</Async.Loading>
    <Async.Fulfilled>
      {data => (
        <div>
          <strong>Loaded some data:</strong>
          <pre>{JSON.stringify(data, null, 2)}</pre>
        </div>
      )}
    </Async.Fulfilled>
    <Async.Rejected>{error => `Something went wrong: ${error.message}`}</Async.Rejected>
  </Async>
)

API

Options

These can be passed in an object to useAsync(), or as props to <Async> and custom instances.

  • promise An already started Promise instance.
  • promiseFn Function that returns a Promise, automatically invoked.
  • deferFn Function that returns a Promise, manually invoked with run.
  • watch Watch a value and automatically reload when it changes.
  • watchFn Watch this function and automatically reload when it returns truthy.
  • initialValue Provide initial data or error for server-side rendering.
  • onResolve Callback invoked when Promise resolves.
  • onReject Callback invoked when Promise rejects.
  • reducer State reducer to control internal state updates.
  • dispatcher Action dispatcher to control internal action dispatching.

useFetch additionally takes these options:

  • defer Force the use of deferFn or promiseFn.
  • json Enable JSON parsing of the response.

promise

Promise

A Promise instance which has already started. It will simply add the necessary resolve/reject callbacks and set startedAt to the time promise was first provided. Changing the value of promise will cancel any pending promise and listen to the new one. If promise is initially undefined, the React Async state will be pending.

Note that reload will not do anything when using promise. Use promiseFn instead.

promiseFn

function(props: Object, controller: AbortController): Promise

A function that returns a promise. It is automatically invoked in componentDidMount and componentDidUpdate. The function receives all component props (or options) and an AbortController instance as arguments.

Be aware that updating promiseFn will trigger it to cancel any pending promise and load the new promise. Passing an arrow function will cause it to change and reload on every render of the parent component. You can avoid this by defining the promiseFn value outside of the render method. If you need to pass variables to the promiseFn, pass them as additional props to <Async>, as promiseFn will be invoked with these props. Alternatively you can use memoization to avoid unnecessary updates.

deferFn

function(args: any[], props: Object, controller: AbortController): Promise

A function that returns a promise. This is invoked only by manually calling run(...args). Receives the same arguments as promiseFn, as well as any arguments to run which are passed through as an array. The deferFn is commonly used to send data to the server following a user action, such as submitting a form. You can use this in conjunction with promiseFn to fill the form with existing data, then updating it on submit with deferFn.

Be aware that when using both promiseFn and deferFn, the shape of their fulfilled value should match, because they both update the same data.

watch

any

Watches this property through componentDidUpdate and re-runs the promiseFn when the value changes, using a simple reference check (oldValue !== newValue). If you need a more complex update check, use watchFn instead.

watchFn

function(props: Object, prevProps: Object): boolean | any

Re-runs the promiseFn when this callback returns truthy (called on every update). Any default props specified by createInstance are available too.

initialValue

any | Error

Initial state for data or error (if instance of Error); useful for server-side rendering.

onResolve

function(data: any): void

Callback function invoked when a promise resolves, receives data as argument.

onReject

function(reason: Error): void

Callback function invoked when a promise rejects, receives rejection reason (error) as argument.

reducer

function(state: any, action: Object, internalReducer: function(state: any, action: Object))

State reducer to take full control over state updates by wrapping the internal reducer. It receives the current state, the dispatched action and the internal reducer. You probably want to invoke the internal reducer at some point.

This is a power feature which loosely follows the state reducer pattern. It allows you to control state changes by intercepting actions before they are handled, or by overriding or enhancing the reducer itself.

dispatcher

function(action: Object, internalDispatch: function(action: Object), props: Object)

Action dispatcher to take full control over action dispatching by wrapping the internal dispatcher. It receives the original action, the internal dispatcher and all component props (or options). You probably want to invoke the internal dispatcher at some point.

This is a power feature similar to the state reducer pattern. It allows you to control state changes by intercepting actions before they are dispatched, to dispatch additional actions, possibly later in time.

defer

boolean

Enables the use of deferFn if true, or enables the use of promiseFn if false. By default this is automatically chosen based on the request method (deferFn for POST / PUT / PATCH / DELETE, promiseFn otherwise).

json

boolean

Enables or disables JSON parsing of the response body. By default this is automatically enabled if the Accept header is set to "application/json".

Render props

<Async> provides the following render props to the children function:

  • data Last resolved promise value, maintained when new error arrives.
  • error Rejected promise reason, cleared when new data arrives.
  • value The value of data or error, whichever was last updated.
  • initialValue The data or error that was provided through the initialValue prop.
  • startedAt When the current/last promise was started.
  • finishedAt When the last promise was fulfilled or rejected.
  • status One of: initial, pending, fulfilled, rejected.
  • isInitial true when no promise has ever started, or one started but was cancelled.
  • isPending true when a promise is currently awaiting settlement. Alias: isLoading
  • isFulfilled true when the last promise was fulfilled with a value. Alias: isResolved
  • isRejected true when the last promise was rejected with a reason.
  • isSettled true when the last promise was fulfilled or rejected (not initial or pending).
  • counter The number of times a promise was started.
  • cancel Cancel any pending promise.
  • run Invokes the deferFn.
  • reload Re-runs the promise when invoked, using any previous arguments.
  • setData Sets data to the passed value, unsets error and cancels any pending promise.
  • 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 (aka loading), false otherwise.

Alias: isLoading

isFulfilled

boolean

true when the last promise was fulfilled (aka resolved) with a value.

Alias: isResolved

isRejected

boolean

true when the last promise was rejected with an error.

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.

cancel

function(): void

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

run

function(...args: any[]): Promise

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

reload

function(): void

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

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.

Helper components

React Async provides several helper components that make your JSX more declarative and less cluttered. They don't have to be direct children of <Async> and you can use the same component several times.

<Initial> / <Async.Initial>

Renders only while the deferred promise is still waiting to be run, or you have not provided any promise.

Props

  • children function(state: Object): Node | Node Render function or React Node.
  • state object Async state object (return value of useAsync()).
  • persist boolean Show until we have data, even while loading or when an error occurred. By default it hides as soon as the promise starts loading.

Examples

const state = useAsync(...)
return (
  <Initial state={state}>
    <p>This text is only rendered while `run` has not yet been invoked on `deferFn`.</p>
  </Initial>
)
<Async deferFn={deferFn}>
  <Async.Initial>
    <p>This text is only rendered while `run` has not yet been invoked on `deferFn`.</p>
  </Async.Initial>
</Async>
<Async.Initial persist>
  {({ error, isPending, run }) => (
    <div>
      <p>This text is only rendered while the promise has not fulfilled yet.</p>
      <button onClick={run} disabled={!isPending}>
        Run
      </button>
      {error && <p>{error.message}</p>}
    </div>
  )}
</Async.Initial>

<Pending> / <Async.Pending>

This component renders only while the promise is pending (aka loading) (unsettled).

Alias: <Async.Loading>

Props

  • children function(state: Object): Node | Node Render function or React Node.
  • state object Async state object (return value of useAsync()).
  • initial boolean Show only on initial load (when data is undefined).

Examples

const state = useAsync(...)
return (
  <Pending state={state}>
    <p>This text is only rendered while performing the initial load.</p>
  </Pending>
)
<Async.Pending initial>
  <p>This text is only rendered while performing the initial load.</p>
</Async.Pending>
<Async.Pending>{({ startedAt }) => `Loading since ${startedAt.toISOString()}`}</Async.Pending>

<Fulfilled> / <Async.Fulfilled>

This component renders only when the promise is fulfilled with data (data !== undefined).

Alias: <Async.Resolved>

Props

  • children function(data: any, state: Object): Node | Node Render function or React Node.
  • state object Async state object (return value of useAsync()).
  • persist boolean Show old data while loading new data. By default it hides as soon as a new promise starts.

Examples

const state = useAsync(...)
return (
  <Fulfilled state={state}>
    {data => <pre>{JSON.stringify(data)}</pre>}
  </Fulfilled>
)
<Async.Fulfilled persist>{data => <pre>{JSON.stringify(data)}</pre>}</Async.Fulfilled>
<Async.Fulfilled>
  {(data, { finishedAt }) => `Last updated ${finishedAt.toISOString()}`}
</Async.Fulfilled>

<Rejected> / <Async.Rejected>

This component renders only when the promise is rejected.

Props

  • children function(error: Error, state: Object): Node | Node Render function or React Node.
  • state object Async state object (return value of useAsync()).
  • persist boolean Show old error while loading new data. By default it hides as soon as a new promise starts.

Examples

const state = useAsync(...)
return <Rejected state={state}>Oops.</Rejected>
<Async.Rejected persist>Oops.</Async.Rejected>
<Async.Rejected>{error => `Unexpected error: ${error.message}`}</Async.Rejected>

<Settled> / <Async.Settled>

This component renders only when the promise is fulfilled or rejected.

Props

  • children function(state: Object): Node | Node Render function or React Node.
  • state object Async state object (return value of useAsync()).
  • persist boolean Show old data or error while loading new data. By default it hides as soon as a new promise starts.

Examples

const state = useAsync(...)
return <Settled state={state}>{state => `Finished at ${state.finishedAt.toISOString()}`</Settled>

Usage examples

Here's several examples to give you an idea of what's possible with React Async. For fully working examples, please check out the examples directory.

Data fetching

This does some basic data fetching, including a loading indicator, error state and retry.

class App extends Component {
  getSession = ({ sessionId }) => fetch(...)

  render() {
    // The promiseFn should be defined outside of render()
    return (
      <Async promiseFn={this.getSession} sessionId={123}>
        {({ data, error, isLoading, reload }) => {
          if (isLoading) {
            return <div>Loading...</div>
          }
          if (error) {
            return (
              <div>
                <p>{error.toString()}</p>
                <button onClick={reload}>try again</button>
              </div>
            )
          }
          if (data) {
            return <pre>{JSON.stringify(data, null, 2)}</pre>
          }
          return null
        }}
      </Async>
    )
  }
}

Form submission

This uses deferFn to trigger an update (e.g. POST / PUT request) after a form submit.

const subscribeToNewsletter = (args, props, controller) => fetch(...)

<Async deferFn={subscribeToNewsletter}>
  {({ error, isLoading, run }) => (
    <form onSubmit={run}>
      <input type="email" name="email" />
      <button type="submit" disabled={isLoading}>
        Subscribe
      </button>
      {error && <p>{error.toString()}</p>}
    </form>
  )}
</Async>

Optimistic updates

This uses both promiseFn and deferFn along with setData to implement optimistic updates.

const updateAttendance = ([attend]) => fetch(...).then(() => attend, () => !attend)

<Async promiseFn={getAttendance} deferFn={updateAttendance}>
  {({ data: isAttending, isLoading, run, setData }) => (
    <Toggle
      on={isAttending}
      onClick={() => {
        setData(!isAttending)
        run(!isAttending)
      }}
      disabled={isLoading}
    />
  )}
</Async>

Server-side rendering

This uses initialValue to enable server-side rendering with Next.js.

static async getInitialProps() {
  // Resolve the promise server-side
  const customers = await loadCustomers()
  return { customers }
}

render() {
  const { customers } = this.props // injected by getInitialProps
  return (
    <Async promiseFn={loadCustomers} initialValue={customers}>
      {({ data, error, isLoading, initialValue }) => { // initialValue is passed along for convenience
        if (isLoading) {
          return <div>Loading...</div>
        }
        if (error) {
          return <p>{error.toString()}</p>
        }
        if (data) {
          return <pre>{JSON.stringify(data, null, 2)}</pre>
        }
        return null
      }}
    </Async>
  )
}

Who's using React Async?

Xebia Intergamma bol.com

Your organization here? Let us know you're using React Async!

Acknowledgements

Versions 1.x and 2.x of react-async on npm are from a different project abandoned years ago. The original author was kind enough to transfer ownership so the react-async package name could be repurposed. The first version of this project is v3.0.0. Many thanks to Andrey Popp for handing over ownership of react-async on npm.

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