A simple, declarative, and composable way to fetch data for React components
A simple, declarative, and composable way to fetch data for React components.
Requires React 0.14 or later.
npm install --save react-refetch
This assumes that you’re using npm package manager with a module bundler like Webpack or Browserify to consume CommonJS modules.
The following ES6 functions are required:
Check the compatibility tables (
Object.assign,
Promise,
fetch,
Array.prototype.find) to make sure all browsers and platforms you need to support have these, and include polyfills as necessary.
See Introducing React Refetch on the Heroku Engineering Blog for background and a quick introduction to this project.
This project was inspired by (and forked from) React Redux. Redux/Flux is a wonderful library/pattern for applications that need to maintain complicated client-side state; however, if your application is mostly fetching and rendering read-only data from a server, it can over-complicate the architecture to fetch data in actions, reduce it into the store, only to select it back out again. The other approach of fetching data inside the component and dumping it in local state is also messy and makes components smarter and more mutable than they need to be. This module allows you to wrap a component in a
connect()decorator like react-redux, but instead of mapping state to props, this lets you map props to URLs to props. This lets you keep your components completely stateless, describe data sources in a declarative manner, and delegate the complexities of data fetching to this module. Advanced options are also supported to lazy load data, poll for new data, and post data to the server.
If you have a component called
Profilethat has a
userIdprop, you can wrap it in
connect()to map
userIdto one or more requests and assign them to new props called
userFetchand
likesFetch:
import React, { Component } from 'react' import { connect, PromiseState } from 'react-refetch'class Profile extends Component { render() { // see below } }
export default connect(props => ({ userFetch:
/users/${props.userId}
, likesFetch:/users/${props.userId}/likes
}))(Profile)
When the component mounts, the requests will be calculated, fetched, and the result will be passed into the component as the props specified. The result is represented as a
PromiseState, which is a synchronous representation of the fetch
Promise. It will either be
pending,
fulfilled, or
rejected. This makes it simple to reason about the fetch state at the point in time the component is rendered:
render() { const { userFetch, likesFetch } = this.propsif (userFetch.pending) { return } else if (userFetch.rejected) { return } else if (userFetch.fulfilled) { return }
// similar for
likesFetch
}
See the composing responses to see how to handle
userFetchand
likesFetchtogether. Although not included in this library because of application-specific defaults, see an example
PromiseStateContainerand its example usage for a way to abstract and simplify the rendering of
PromiseStates.
When new props are received, the requests are re-calculated, and if they changed, the data is refetched and passed into the component as new
PromiseStates. Using something like React Router to derive the props from the URL in the browser, the application can control state changes just by changing the URL. When the URL changes, the props change, which recalculates the requests, new data is fetched, and it is reinjected into the components:
By default, the requests are compared using their URL, headers, and body; however, if you want to use a custom value for the comparison, set the
comparisonattribute on the request. This can be helpful when the request should or should not be refetched in response to a prop change that is not in the request itself. A common situation where this occurs is when two different requests should be refetched together even though one of the requests does not actually include the prop. Note, this is using the request object syntax for
userStatsFetchinstead of just a plain URL string. This syntax allows for more advanced options. See the API documentation for details:
connect(props => ({ usersFetch: `/users?status=${props.status}&page=${props.page}`, userStatsFetch: { url: `/users/stats`, comparison: `${props.status}:${props.page}` } }))(UsersList)
In this example,
usersFetchis refetched every time
props.statusor
props.pagechanges because the URL is changed. However,
userStatsFetchdoes not contain these props in its URL, so would not normally be refetched, but because we added
comparison: ${props.status}:${props.page}, it will be refetched along with
usersFetch. In general, you should only rely on changes to the requests themselves to control when data is refetched, but this technique can be helpful when finer-grained control is needed.
If you always want data to be refetched when any new props are received, set the
force: trueoption on the request. This will take precedence over any custom
comparisonand the default request comparison. For example:
connect(props => ({ usersFetch: `/users?status=${props.status}&page=${props.page}`, userStatsFetch: { url: `/users/stats`, force: true } }))(UsersList)
Setting
force: trueshould be avoid if at all possible because it could result in extraneous data fetching and rendering of the component. Try to use the default comparison or custom
comparisonoption instead.
If the
refreshIntervaloption is provided along with a URL, the data will be refreshed that many milliseconds after the last successful response. If a request was ever rejected, it will not be refreshed or otherwise retried. In this example,
likesFetchwill be refreshed every minute. Note, this is using the request object syntax for
likeFetchinstead of just a plain URL string. This syntax allows for more advanced options. See the API documentation for details.
connect(props => ({ userFetch:`/users/${props.userId}`, likesFetch: { url: `/users/${props.userId}/likes`, refreshInterval: 60000 } }))(Profile)
When refreshing, the
PromiseStatewill be the same as a the previous
fulfilledstate, but with the
refreshingattribute set. That is,
pendingwill remain unset and the existing
valuewill be left in tact. When the refresh completes,
refreshingwill be unset and the
valuewill be updated with the latest data. If the refresh is rejected, the
PromiseStatewill move into a
rejectedand not attempt to refresh again.
Instead of mapping the props directly to a URL string or request object, you can also map the props to a function that returns a URL string or request object. When the component receives props, instead of the data being fetched immediately and injected as a
PromiseState, the function is bound to the props and injected into the component as functional prop to be called later (usually in response to a user action). This can be used to either lazy load data, post data to the server, or refresh data. These are best shown with examples:
Here is a simple example of lazy loading the
likesFetchwith a function:
connect(props => ({ userFetch: `/users/${props.userId}`, lazyFetchLikes: max => ({ likesFetch: `/users/${props.userId}/likes?max=${max}` }) }))(Profile)
In this example,
userFetchis fetched normally when the component receives props, but
lazyFetchLikesis a function that returns
likesFetch, so nothing is fetched immediately. Instead
lazyFetchLikesis injected into the component as a function to be called later inside the component:
this.props.lazyFetchLikes(10)
When this function is called, the request is calculated using both the bound props and any passed in arguments, and the
likesFetchresult is injected into the component normally as a
PromiseState.
Functions can also be used for post data to the server in response to a user action. For example:
connect(props => ({ postLike: subject => ({ postLikeResponse: { url: `/users/${props.userId}/likes`, method: 'POST', body: JSON.stringify({ subject }) } }) }))(Profile)
The
postLikefunction is injected in as a prop, which can then be tied to a button:
this.props.postLike(someSubject)}>Like!
When the user clicks the button,
someSubjectis posted to the URL and the response is injected as a new
postLikeResponseprop as a
PromiseStateto show progress and feedback to the user.
Functions can also be used to manually refresh data by overwriting an existing
PromiseState:
connect(props => { const url = `/users/${props.userId}`return { userFetch: url, refreshUser: () => ({ userFetch: { url, force: true, refreshing: true } }) } })(Profile)
The
userFetchdata is first loaded normally when the component receives props, but the
refreshUserfunction is also injected into the component. When
this.props.refreshUser()is called, the request is calculated, and compared with the existing
userFetchrequest. If the request changed (or
force: true), the data is refetched and the existing
userFetch
PromiseStateis overwritten. This should generally only be used for user-invoked refreshes; see above for automatically refreshing on an interval.
Note, the example above sets
force: trueand
refreshing: trueon the request returned by the
refreshUser()function. These attributes are optional, but commonly used with manual refreshes.
force: trueavoids the default request comparison (e.g.
url,
method,
headers,
body) with the existing
userFetchrequest so that every time
this.props.refreshUser()is called, a fetch is performed. Because the request would not have changed from the last prop change in the example above,
force: trueis required in this case for the fetch to occur when
this.props.refreshUser()is called.
refreshing: trueavoids the existing
PromiseStatefrom being cleared while fetch is in progress.
The two examples above can be combined to post data to the server and refresh an existing
PromiseState. This is a common pattern when a responding to a user action to update a resource and reflect that update in the component. For example, if
PATCH /users/:user_idresponds with the updated user, it can be used to overwrite the existing
userFetchwhen the user updates her name:
connect(props => ({ userFetch: `/users/${props.userId}`, updateUser: (firstName, lastName) => ({ userFetch: { url: `/users/${props.userId}` method: 'PATCH' body: JSON.stringify({ firstName, lastName }) } }) }))(Profile)
If a component needs data from more than one URL, the
PromiseStates can be combined with
PromiseState.all()to be
pendinguntil all the
PromiseStates have been fulfilled. For example:
render() { const { userFetch, likesFetch } = this.props// compose multiple PromiseStates together to wait on them as a whole const allFetches = PromiseState.all([userFetch, likesFetch])
// render the different promise states if (allFetches.pending) { return } else if (allFetches.rejected) { return } else if (allFetches.fulfilled) { // decompose the PromiseState back into individual const [user, likes] = allFetches.value return (
) } }
Similarly,
PromiseState.race()can be used to return the first settled
PromiseState. Like their asynchronous
Promisecounterparts,
PromiseStatescan be chained with
then()and
catch(); however, the handlers are run immediately to transform the existing state. This can be helpful to handle errors or transform values as part of a composition. For example, to provide a fallback value to
likesFetchin the case of failure:
PromiseState.all([userFetch, likesFetch.catch(reason => [])])
Inside of
connect(), requests can be chained using
then(),
catch(),
andThen()and
andCatch()to trigger additional requests after a previous request is fulfilled. These are not to be confused with the similar sounding functions on
PromiseState, which are on the response side, are synchronous, and are executed for every change of the
PromiseState.
then()is helpful for cases where multiple requests are required to get the data needed by the component and the subsequent request relies on data from the previous request. For example, if you need to make a request to
/foos/${name}to look up
foo.idand then make a second request to
/bar-for-foos-by-id/${foo.id}and return the whole thing as
barFetch(the component will not have access to the intermediate
foo):
connect(({ name }) => ({ barFetch: { url: `/foos/${name}`, then: foo => `/bar-for-foos-by-id/${foo.id}` } }))
andThen()is similar, but is intended for side effect requests where you still need access to the result of the first request and/or need to fanout to multiple requests:
connect(({ name }) => ({ fooFetch: { url: `/foos/${name}`, andThen: foo => ({ barFetch: `/bar-for-foos-by-id/${foo.id}` }) } }))
This is also helpful for cases where a fetch function is changing data that is in some other fetch that is a collection. For example, if you have a list of
foos and you create a new
fooand the list needs to be refreshed:
connect(({ name }) => ({ foosFetch: '/foos', createFoo: name => ({ fooCreation: { method: 'POST', url: '/foos', andThen: () => ({ foosFetch: { url: '/foos', refreshing: true } }) } }) }))
catchand
andCatchare similar, but for error cases.
To support static data and response transformations, there is a special kind of request called an "identity request" that has a
valueinstead of a
url. The
valueis passed through directly to the
PromiseStatewithout actually fetching anything. In its pure form, it looks like this:
connect(props => ({ usersFetch: { value: [ { id: 1, name: 'Jane Doe', verified: true }, { id: 2, name: 'John Doe', verified: false } ] } }))(Users)
In this case, the
usersFetch
PromiseStatewill be set to the provided list of users. The use case for identity requests by themselves is limited to mostly injecting static data during development and testing; however, they can be quite powerful when used with request chaining. For example, it is possible to fetch data from the server, filter it within a
thenfunction, and return an identity request:
connect(props => ({ usersFetch: { url: `/users`, then: (users) => ({ value: users.filter(u => u.verified) }) } }))(Users)
Note, this form of transformation is similar to what is possible on the
PromiseState(i.e.
this.props.usersFetch.then(users => users.filter(u => u.verified))); however, this has the advantage of only being called when
usersFetchchanges and keeps the logic out of the component.
Identity requests can also be provided a
Promise(or any "thenable") or a
Function. If
valueis a
Promise, the
PromiseStatewill be
pendinguntil the
Promiseis resolved. This can be helpful for asynchronous, non-fetch operations (e.g. file i/o) that want to use a similar pattern as fetch operations. If
valueis a
Function, it will be evaluated with no arguments and its return value will be used instead, as in cases described above. The
Functionwill be only be called when
comparisonchanges. This can be helpful for cases where you want to provide an identify request, but it is expensive to evaluate. By wrapping it in a function, it is only evaluated when something changes.
connect(props => ({ userFetch: { comparison: props.userId, value: () => SomeExternalAPI.getUser(`/users/${props.userId}`) } }))(Users)
Both request and response headers and other metadata are accessible. Custom request headers can be set on the request as an object:
connect(props => ({ userFetch: { url: `/users/${props.userId}`, headers: { FOO: 'foo', BAR: 'bar' } } }))(Profile)
Requestand
Responsecan be accessed via the
metaattribute on the
PromiseState. For example, to access the a response header:
userFetch.meta.response.headers.get('FOO')
Do not attempt to read bodies directly from
meta.requestor
meta.response. They are provided for metadata purposes only.
It is possible to modify the various defaults used by React Refetch, as well as substitute in custom implementations of internal functions. A simple use case would be to avoid repeating the same option for every fetch block:
import { connect } from 'react-refetch' const refetch = connect.defaults({ credentials: 'include' })refetch(props => ({ userFetch:
/users/${props.userId}
}))(Profile)
A more advanced use case would be to replace the
buildRequestinternal function to, for example, modify headers on the fly based on the URL of the request, or using advanced
Requestoptions:
// api-connector.js import { connect } from 'react-refetch' import urlJoin from 'url-join' import { getPrivateToken } from './api-tokens'const baseUrl = 'https://api.example.com/'
export default connect.defaults({ buildRequest: function (mapping) { const options = { method: mapping.method, cache: 'force-cache', referrer: 'https://example.com', headers: mapping.headers, credentials: mapping.credentials, redirect: mapping.redirect, mode: mapping.mode, body: mapping.body }
if (mapping.url.match(/private/)) { options.headers['X-Api-Token'] = getPrivateToken() } if (mapping.url.match(/listOfServers.json$/)) { options.integrity = 'sha256-BpfBw7ivV8q2jLiT13fxDYAe2tJllusRSZ273h2nFSE=' } return new Request(urlJoin(baseUrl, mapping.url), options)
} })
// ProfileComponent.js import connect from './api-connector' connect(props => ({ userFetch:
/users/${props.userId}
, serversFetch:/listOfServers.json
}))(Profile)
You can also replace the
handleResponsefunction, which takes a
Response, and should return a Promise that resolves to the value of the response, or rejects based on the body, headers, status code, etc. You can use it, for example, to parse CSV instead of JSON:
// api-connector.js import { connect } from 'react-refetch' import { parse } from 'csv'const csvConnector = connect.defaults({ handleResponse: function (response) { if (response.headers.get('content-length') === '0' || response.status === 204) { return }
const csv = response.text() if (response.status >= 200 && response.status < 300) { return csv.then(text => new Promise((resolve, reject) => { parse(text, (err, data) => { if (err) { reject(err) } resolve(data) }) })) } else { return csv.then(cause => Promise.reject(new Error(cause))) }
} })
csvConnector(props => ({ userFetch:
/users/${props.userId}.csv
}))(Profile)
fetchand
Requestimplementations
Through this same API it is possible to change the internal
fetchand
Requestimplementations. This could be useful for a number of reasons, such as precise control over requests or customisation that is not possible with either
buildRequestor
handleResponse.
For example, here's a simplistic implementation of a "caching fetch," which will cache the result of successful requests for a minute, regardless of headers:
import { connect } from 'react-refetch'const cache = new Map() function cachingFetch(input, init) { const req = new Request(input, init) const now = new Date().getTime() const oneMinuteAgo = now - 60000 const cached = cache.get(req.url)
if (cached && cached.time < oneMinuteAgo) { return new Promise(resolve => resolve(cached.response.clone())) }
return fetch(req).then(response => { cache.set(req.url, { time: now, response: response.clone() })
return response
}) }
connect.defaults({ fetch: cachingFetch })(props => ({ userFetch:
/users/${props.userId}
}))(Profile)
When using this feature, make sure to read the
fetchAPI and interface documentation and all related topics. Notably, you need to keep in mind that the
bodyof a
Responsecan only be consumed once, so if you need to read it in your custom
fetch, you also need to recreate a brand new
Response(or a
.clone()of the original one if you're not modifying the body) so React Refetch can work properly.
This is an advanced feature. Use existing declarative functionality wherever possible. Customise
buildRequestor
handleResponseif these can work instead. Please be aware that changing the
fetch(or
Request) implementation could conflict with built-in current or future functionality.
For unit testing components connected, a non-default export of the unconnected component can be exposed to allow unit tests to inject their own
PromiseState(s) as props. This allows for unit tests to test both success and error scenarios without having to deal with mocking HTTP, timing of responses, or other details about how the
PromiseState(s) is fulfilled -- instead, they can just focus on asserting that the component itself renders the
PromiseState(s) correctly in various scenarios.
The recommended naming convention for the unconnected component is to prepend an underscore to the component name. For example, if there is a component called
Profile, add a non-default export of
_Profilebefore the default export with
connect:
class Profile extends React.Component { static propTypes = { userFetch: PropTypes.instanceOf(PromiseState).isRequired, }render() { const { userFetch } = this.props
if (userFetch.pending) { return <loadinganimation></loadinganimation> } else if (userFetch.rejected) { return <errorbox error="{userFetch.reason}/"> } else if (userFetch.fulfilled) { return <user user="{userFetch.value}/"> }
} }
export { Profile as _Profile }
export default connect(props => ({ userFetch:
/users/${props.userId}
}))(Profile)
Now, unit tests can use the static methods on
PromiseStateto inject their own
PromiseState(s) as props. For example, here is a unit test using Enzyme to shallow render the unconnected
_Profileand provides a pending
PromiseStateand asserts that the
LoadingAnimationis present:
const c = shallow( <_profile userfetch="{PromiseState.create()}"> )expect(wrapper.find(LoadingAnimation)).to.have.length(1)
Similarly, the rejected and fulfilled cases can be tested:
const expectedError = new Error('boom')const c = shallow( <_profile userfetch="{PromiseState.reject(expectedError)}"></_profile> )
expect(c.find(ErrorBox).first().prop().error).toEqual(expectedError)
const user = new User()const c = shallow( <_profile userfetch="{PromiseState.resolve(user)}"></_profile> )
expect(wrapper.find(User)).to.have.length(1)
This is a complex example demonstrating various feature at once:
import React, { Component, PropTypes } from 'react' import { connect, PromiseState } from 'react-refetch'class Profile extends React.Component { static propTypes = { params: PropTypes.shape({ userId: PropTypes.string.isRequired, }).isRequired, userFetch: PropTypes.instanceOf(PromiseState).isRequired likesFetch: PropTypes.instanceOf(PromiseState).isRequired updateStatus: PropTypes.func.isRequired updateStatusResponse: PropTypes.instanceOf(PromiseState) // will not be set until after
updateStatus()
is called }render() { const { userFetch, likesFetch } = this.props
) }// compose multiple PromiseStates together to wait on them as a whole const allFetches = PromiseState.all([userFetch, likesFetch]) // render the different promise states if (allFetches.pending) { return <loadinganimation></loadinganimation> } else if (allFetches.rejected) { return <error error="{allFetches.reason}/"> } else if (allFetches.fulfilled) { // decompose the PromiseState back into individual const [user, likes] = allFetches.value return ( <div> <user data="{user}/"> <likes data="{likes}/"> </likes></user>
// call `updateStatus()` on button click <button onclick="{()"> { this.props.updateStatus("Hello World")} }>Update Status</button> if (updateStatusResponse) { // render the different promise states, but will be `null` until `updateStatus()` is called }
} }
// declare the requests for fetching the data, assign them props, and connect to the component. export default connect(props => { return { // simple GET from a URL injected as
userFetch
prop // ifuserId
changes, data will be refetched userFetch:/users/${props.params.userId}
,// similar to `userFetch`, but using object syntax // specifies a refresh interval to poll for new data likesFetch: { url: `/users/${props.userId}/likes`, refreshInterval: 60000 }, // declaring a request as a function // not immediately fetched, but rather bound to the `userId` prop and injected as `updateStatus` prop // when `updateStatus` is called, the `status` is posted and the response is injected as `updateStatusResponse` prop. updateStatus: status => ({ updateStatusResponse: { url: `/users/${props.params.userId}/status`, method: 'POST', body: status } })
} })(Profile)
If you are using React Refetch in a project that is using TypeScript, this library ships with type definitions.
Below is example connected component in TypeScript. Note how there is both an
OuterPropsand
InnerProps. The
OuterPropare the props the component receives from the outside. In this example, the
OuterPropswould just be
userId: stringthe caller is expected to pass in (e.g. ). The
InnerPropsare the
PromiseStateprops that the
connect()function injects into the component when fetching data. Since the
InnerPropsinclude the
OuterProps, they are defined as
InnerProps extends OuterPropsand then the component itself
extends React.Component. This allows the component to have access to both the
userId: stringand
userFetch: PromiseStateinternally. However, the
connectfunction returns a component with only the
OuterProps(e.g.
React.Component) so callers only need to pass in
userId: string.
interface OuterProps { userId: string }interface InnerProps extends OuterProps { userFetch: PromiseState }
class UserWidget extends React.Component { render() { return (
export default connect((props) => ({
userFetch: /users/${props.userId}
}))(UserWidget)
This software is provided "as is", without warranty or support of any kind, express or implied. See license for details.